Method and apparatus for sharing signals on a single channel

ABSTRACT

A method and apparatus for transmitting two signals on a single channel comprising a single frequency and a single time slot are disclosed. The method includes: generating a first training sequence from a first set of training sequences; generating a second training sequence from a second set of training sequences. The first and second training sequences have a low cross-correlation ratio with respect to each other; and the second set of training sequences is different from the first set of training sequences. First and second data are generated. The first data is combined with the first training sequence to produce first combined data and the second data is combined with the second training sequence to produce second combined data. The first and second combined data are transmitted on the single channel by a single transmitting apparatus.

FIELD OF THE INVENTION

The invention relates generally to the field of radio communications andin particular to the increasing of channel capacity in a radiocommunications system.

BACKGROUND

More and more people are using mobile communication devices, such as,for example, mobile phones, not only for voice but also for datacommunications. In the GSM/EDGE Radio Access Network (GERAN)specification, GPRS and EGPRS provide data services. The standards forGERAN are maintained by the 3GPP (Third Generation Partnership Project).GERAN is a part of Global System for Mobile Communications (GSM). Morespecifically, GERAN is the radio part of GSM/EDGE together with thenetwork that joins the base stations (the A_(ter) and A_(bis)interfaces) and the base station controllers (A interfaces, etc.). GERANrepresents the core of a GSM network. It routes phone calls and packetdata from and to the PSTN and Internet and to and from remote stations,including mobile stations. UMTS (Universal Mobile TelecommunicationsSystem) standards have been adopted in GSM systems, for third-generationcommunication systems employing larger bandwidths and higher data rates.GERAN is also a part of combined UMTS/GSM networks.

The following issues are present in today's networks. First, moretraffic channels are needed which is a capacity issue. Since there is ahigher demand of data throughput on the downlink (DL) than on the uplink(UL), the DL and UL usages are not symmetrical. For example a mobilestation (MS) doing FTP transfer is likely to be given 4D1U, which couldmean that it takes four users resources for full rate, and eight usersresources for half rate. As it stands at the moment, the network has tomake a decision whether to provide service to 4 or 8 callers on voice or1 data call. More resources will be necessary to enable DTM (dualtransfer mode) where both data calls and voice calls are made at thesame time.

Second, if a network serves a data call while many new users also wantvoice calls, the new users will not get service unless both UL and DLresources are available. Therefore some UL resource could be wasted. Onone hand there are customers waiting to make calls and no service can bemade; on the other hand the UL is available but wasted due to lack ofpairing DL.

Third, there is less time for UEs working in multi-timeslot mode to scanneighbor cells and monitor them, which may cause call drops andperformance issues.

FIG. 1 shows a block diagram of a transmitter 118 and a receiver 150 ina wireless communication system. For the downlink, the transmitter 118may be part of a base station, and receiver 150 may be part of awireless device (remote station). For the uplink, the transmitter 118may be part of a wireless device, and receiver 150 may be part of a basestation. A base station is generally a fixed station that communicateswith the wireless devices and may also be referred to as a Node B, anevolved Node B (eNode B), an access point, etc. A wireless device may bestationary or mobile and may also be referred to as a mobile station, auser equipment, a mobile equipment, a terminal, a remote terminal, anaccess terminal, a station, remote station etc. A wireless device may bea cellular phone, a personal digital assistant (PDA), a wireless modem,a wireless communication device, a handheld device, a subscriber unit, alaptop computer, etc.

At transmitter 118, a transmit (TX) data processor 120 receives andprocesses (e.g., formats, encodes, and interleaves) data and providescoded data. A modulator 130 performs modulation on the coded data andprovides a modulated signal. Modulator 130 may perform Gaussian minimumshift keying (GMSK) for GSM, 8-ary phase shift keying (8-PSK) forEnhanced Data rates for Global Evolution (EDGE), etc. GMSK is acontinuous phase modulation protocol whereas 8-PSK is a digitalmodulation protocol. A transmitter unit (TMTR) 132 conditions (e.g.,filters, amplifies, and upconverts) the modulated signal and generatesan RF modulated signal, which is transmitted via an antenna 134.

At receiver 150, an antenna 152 receives RF modulated signals fromtransmitter 110 and other transmitters. Antenna 152 provides a receivedRF signal to a receiver unit (RCVR) 154. Receiver unit 154 conditions(e.g., filters, amplifies, and downconverts) the received RF signal,digitizes the conditioned signal, and provides samples. A demodulator160 processes the samples as described below and provides demodulateddata. A receive (RX) data processor 170 processes (e.g., deinterleavesand decodes) the demodulated data and provides decoded data. In general,the processing by demodulator 160 and RX data processor 170 iscomplementary to the processing by modulator 130 and TX data processor120, respectively, at transmitter 110.

Controllers/processors 140, 180 direct operation at transmitter 118 andreceiver 150, respectively. Memories 142, 182 store program codes in theform of computer software and data used by transmitter 118 and receiver150, respectively.

FIG. 2 shows a block diagram of a design of receiver unit 154 anddemodulator 160 at receiver 150 in FIG. 1. Within receiver unit 154, areceive chain 440 processes the received RF signal and provides I and Qbaseband signals, which are denoted as I_(bb) and Q_(bb). Receive chain440 may perform low noise amplification, analog filtering, quadraturedownconversion, etc. An analog-to-digital converter (ADC) 442 digitizesthe I and Q baseband signals at a sampling rate of f_(adc) and providesI and Q samples, which are denoted as I_(adc) and Q_(adc). In general,the ADC sampling rate f_(adc) may be related to the symbol rate f_(sym)by any integer or non-integer factor.

Within demodulator 160, a pre-processor 420 performs pre-processing onthe I and Q samples from ADC 442. For example, pre-processor 420 mayremove direct current (DC) offset, remove frequency offset, etc. Aninput filter 422 filters the samples from pre-processor 420 based on aparticular frequency response and provides input I and Q samples, whichare denoted as I_(in) and Q_(in). Filter 422 may filter the I and Qsamples to suppress images resulting from the sampling by ADC 442 aswell as jammers. Filter 422 may also perform sample rate conversion,e.g., from 24× oversampling down to 2× oversampling. A data filter 424filters the input I and Q samples from input filter 422 based on anotherfrequency response and provides output I and Q samples, which aredenoted as I_(out) and Q_(out). Filters 422 and 424 may be implementedwith finite impulse response (FIR) filters, infinite impulse response(IIR) filters, or filters of other types. The frequency responses offilters 422 and 424 may be selected to achieve good performance. In onedesign, the frequency response of filter 422 is fixed, and the frequencyresponse of filter 424 is configurable.

An adjacent channel interference (ACI) detector 430 receives the input Iand Q samples from filter 422, detects for ACI in the received RFsignal, and provides an ACI indicator to filter 424. The ACI indicatormay indicates whether or not ACI is present and, if present, whether theACI is due to the higher RF channel centered at +200 KHz and/or thelower RF channel centered at −200 KHz. The frequency response of filter424 may be adjusted based on the ACI indicator, as described below, toachieve good performance.

An equalizer/detector 426 receives the output I and Q samples fromfilter 424 and performs equalization, matched filtering, detection,and/or other processing on these samples. For example,equalizer/detector 426 may implement a maximum likelihood sequenceestimator (MLSE) that determines a sequence of symbols that is mostlikely to have been transmitted given a sequence of I and Q samples anda channel estimate.

The Global System for Mobile Communications (GSM) is a widespreadstandard in cellular, wireless communication. GSM employs a combinationof Time Division Multiple Access (TDMA) and Frequency Division MultipleAccess (FDMA) for the purpose of sharing the spectrum resource. GSMnetworks typically operate in a number of frequency bands. For example,for uplink communication, GSM-900 commonly uses a radio spectrum in the890-915 MHz bands (Mobile Station to Base Transceiver Station). Fordownlink communication, GSM 900 uses 935-960 MHz bands (base station tomobile station). Furthermore, each frequency band is divided into 200kHz carrier frequencies providing 124 RF channels spaced at 200 kHz.GSM-1900 uses the 1850-1910 MHz bands for the uplink and 1930-1990 MHzbands for the downlink. Like GSM 900, FDMA operates to divide theGSM-1900 spectrum for both uplink and downlink into 200 kHz-wide carrierfrequencies. Similarly, GSM-850 uses the 824-849 MHz bands for theuplink and 869-894 MHz bands for the downlink, while GSM-1800 uses the1710-1785 MHz bands for the uplink and 1805-1880 MHz bands for thedownlink.

Each channel in GSM is identified by a specific radio frequency channelidentified by an Absolute Radio Frequency Channel Number (ARFCN). Forexample, ARFCNs 1-124 are assigned to the channels of GSM 900, whileARFCNs 512-810 are assigned to the channels of GSM 1900. Similarly,ARFCNs 128-251 are assigned to the channels of GSM 850, while ARFCNs512-885 are assigned to the channels of GSM 1800. Also, each basestation is assigned one or more carrier frequencies. Each carrierfrequency is divided into eight time slots (which are labeled as timeslots 0 through 7) using TDMA such that eight consecutive time slotsform one TDMA frame with a duration of 4.615 ms. A physical channeloccupies one time slot within a TDMA frame. Each active wirelessdevice/user is assigned one or more time slot indices for the durationof a call. User-specific data for each wireless device is sent in thetime slot(s) assigned to that wireless device and in TDMA frames usedfor the traffic channels.

Each time slot within a frame is used for transmitting a “burst” of datain GSM. Sometimes the terms time slot and burst may be usedinterchangeably. Each burst includes two tail fields, two data fields, atraining sequence (or midamble) field, and a guard period (GP). Thenumber of symbols in each field is shown inside the parentheses. A burstincludes 148 symbols for the tail, data, and midamble fields. No symbolsare sent in the guard period. TDMA frames of a particular carrierfrequency are numbered and formed in groups of 26 or 51 TDMA framescalled multi-frames.

FIG. 3 shows example frame and burst formats in GSM. The timeline fortransmission is divided into multiframes. For traffic channels used tosend user-specific data, each multiframe in this example includes 26TDMA frames, which are labeled as TDMA frames 0 through 25. The trafficchannels are sent in TDMA frames 0 through 11 and TDMA frames 13 through24 of each multiframe. A control channel is sent in TDMA frame 12. Nodata is sent in idle TDMA frame 25, which is used by the wirelessdevices to make measurements for neighbor base stations.

FIG. 4 shows an example spectrum in a GSM system. In this example, fiveRF modulated signals are transmitted on five RF channels that are spacedapart by 200 KHz. The RF channel of interest is shown with a centerfrequency of 0 Hz. The two adjacent RF channels have center frequenciesthat are +200 KHz and −200 KHz from the center frequency of the desiredRF channel. The next two nearest RF channels (which are referred to asblockers or non-adjacent RF channels) have center frequencies that are+400 KHz and −400 KHz from the center frequency of the desired RFchannel. There may be other RF channels in the spectrum, which are notshown in FIG. 3 for simplicity. In GSM, an RF modulated signal isgenerated with a symbol rate of f_(sym)=13000/40=270.8 kilosymbols/second (Ksps) and has a −3 dB bandwidth of up to ±135 KHz. TheRF modulated signals on adjacent RF channels may thus overlap oneanother at the edges, as shown in FIG. 4.

One or more modulation schemes are used in GSM to communicateinformation such as voice, data, and/or control information. Examples ofthe modulation schemes may include GMSK (Gaussian Minimum Shift Keying),M-ary QAM (Quadrature Amplitude Modulation) or M-ary PSK (Phase ShiftKeying), where M=2^(n), with n being the number of bits encoded within asymbol period for a specified modulation scheme. GMSK, is a constantenvelope binary modulation scheme allowing raw transmission at a maximumrate of 270.83 kilobits per second (Kbps).

GSM is efficient for standard voice services. However, high-fidelityaudio and data services desire higher data throughput rates due toincreased demand on capacity to transfer both voice and data services.To increase capacity, the General Packet Radio Service (GPRS), EDGE(Enhanced Data rates for GSM Evolution) and UMTS (Universal MobileTelecommunications System) standards have been adopted in GSM systems.

General Packet Radio Service (GPRS) is a non-voice service. It allowsinformation to be sent and received across a mobile telephone network.It supplements Circuit Switched Data (CSD) and Short Message Service(SMS). GPRS employs the same modulation schemes as GSM. GPRS allows foran entire frame (all eight time slots) to be used by a single mobilestation at the same time. Thus, higher data throughput rates areachievable.

The EDGE standard uses both the GMSK modulation and 8-PSK modulation.Also, the modulation type can be changed from burst to burst. 8-PSKmodulation in EDGE is a linear, 8-level phase modulation with 3π/8rotation, while GMSK is a non-linear, Gaussian-pulse-shaped frequencymodulation. However, the specific GMSK modulation used in GSM can beapproximated with a linear modulation (i.e., 2-level phase modulationwith a π/2 rotation). The symbol pulse of the approximated GMSK and thesymbol pulse of 8-PSK are identical.

In GSM/EDGE, frequency bursts (FB) are sent regularly by the BaseStation (BS) to allow Mobile Stations (MS) to synchronize their LocalOscillator (LO) to the Base Station LO, using frequency offsetestimation and correction. These bursts comprise a single tone, whichcorresponds to an all “0” payload and training sequence. The all zeropayload of the frequency burst is a constant frequency signal, or asingle tone burst. When in power-on or camp-on mode or when firstaccessing the network, the remote station hunts continuously for afrequency burst from a list of carriers.

Upon detecting a frequency burst, the remote station will estimate thefrequency offset relative to its nominal frequency, which is 67.7 KHzfrom the carrier. The remote station LO will be corrected using thisestimated frequency offset. In power-on mode, the frequency offset canbe as much as +/−19 KHz. The remote station will periodically wake up tomonitor the frequency burst to maintain its synchronization in standbymode. In the standby mode, the frequency offset is within ±2 KHz.

Modern mobile cellular telephones are able to provide conventional voicecalls and data calls. The demand for both types of calls continues toincrease, placing increasing demands on network capacity. Networkoperators address this demand by increasing their capacity. This isachieved for example by dividing or adding cells and hence adding morebase stations, which increases hardware costs. It is desirable toincrease network capacity without unduly increasing hardware costs, inparticular to cope with unusually large peak demand during major eventssuch as an international football match or a major festival, in whichmany users or subscribers who are located within a small area wish toaccess the network at one time.

When a first remote station is allocated a channel for communication (achannel comprising a channel frequency and a time slot), a second remotestation can only use the allocated channel after the first remotestation has finished using the channel. Maximum cell capacity is reachedwhen all the allocated channel frequencies are used in the cell and allavailable time slots are either in use or allocated. This means that anyadditional remote station user will not be able to get service. Inreality, another capacity limit exists due to co-channel interferences(CCI) and adjacent channel interferences (ACI) introduced by highfrequency re-use pattern and high capacity loading (such as 80% oftimeslots and channel frequencies).

Network operators have increased capacity in a number of ways, all ofwhich require added resources and added cost. For example, one approachis to divide cells into sectors by using sectored, or directional,antenna arrays. Each sector can provide communications for a subset ofremote stations within the cell and the interference between remotestations in different sectors is less than if the cell were not dividedinto sectors and all the remote stations were in the same cell.

Another approach is to divide cells into smaller cells, each new smallercell having a base station. Both these approaches are expensive toimplement due to added network equipment. In addition, adding cells ordividing cells into several smaller cells can result in remote stationswithin one cell experiencing more CCI and ACI interference fromneighboring cells because the distance between cells is reduced.

Another approach is to . . . (use the same TS for two MS by a basestation in the same cell

SUMMARY OF THE INVENTION

A method and apparatus for transmitting two signals on the same channelis defined in the appended claims.

Further scope of the applicability of the present method and apparatuswill become apparent from the following detailed description, claims,and drawings. However, it should be understood that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the scope of theinvention will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a transmitter and a receiver.

FIG. 2 shows a block diagram of a receiver unit and a demodulator.

FIG. 3 shows example frame and burst formats in GSM.

FIG. 4 shows an example spectrum in a GSM system.

FIG. 5 is a simplified representation of a cellular communicationssystem;

FIG. 6 shows an arrangement of cells which are part of a cellularsystem;

FIG. 7 shows an example arrangement of time slots for a time divisionmultiple access (TDMA) communications system;

FIG. 8A shows an apparatus for operating in a multiple accesscommunication system to produce first and second signals sharing asingle channel;

FIG. 8B shows an apparatus for operating in a multiple accesscommunication system to produce first and second signals sharing asingle channel and using a combiner to combine first and secondmodulated signals;

FIG. 9 of the accompanying drawings is a flowchart disclosing a methodfor using the apparatus shown in any of FIG. 8, 10 or 11 of theaccompanying drawings;

FIG. 10A shows an example embodiment wherein the method described byFIG. 9 would reside in the base station controller;

FIG. 10B is a flowchart disclosing the steps executed by the basestation controller of FIG. 10A;

FIG. 11 shows a base station in aspects illustrating the flow of signalsin a base station;

FIG. 12 shows example arrangements for data storage within a memorysubsystem which might reside within a base station controller (BSC) of acellular communication system.

FIG. 13 shows an example receiver architecture for a remote stationhaving the DARP feature of the present method and apparatus;

FIG. 14 shows part of a GSM system adapted to assign the same channel totwo remote stations;

FIG. 15 shows a flowchart disclosing the steps executed when using thecomplimentary training sequences of the present method and apparatus;

FIG. 16 shows a base station with software stored in memory which mayexecute the methods disclosed in this patent application;

FIG. 17 contains a test result summary for 1% FER when pairing legacytraining sequences with training sequences of the QCOM7 set of TSCs;

FIG. 18 contains a test result summary for 1% FER when pairing legacyTSCs with QCOM8 TSCs;

FIG. 19 is a performance plot when pairing QCOM7 TSC0 with legacy TSC0;

FIG. 20 is a performance plot when pairing QCOM7 TSC1 with legacy TSC1;

FIG. 21 is a performance plot when pairing QCOM7 TSC2 with legacy TSC2;

FIG. 22 is a performance plot when pairing QCOM7 TSC3 with legacy TSC3;

FIG. 23 is a performance plot when pairing QCOM7 TSC4 with legacy TSC4;

FIG. 24 is a performance plot when pairing QCOM7 TSC5 with legacy TSC5;

FIG. 25 is a performance plot when pairing QCOM7 TSC6 with legacy TSC6;

FIG. 26 is a performance plot when pairing QCOM7 TSC7 with legacy TSC7;

FIG. 27 is a performance plot when pairing QCOM8 TSC0 with legacy TSC0;

FIG. 28 is a performance plot when pairing QCOM8 TSC1 with legacy TSC1;

FIG. 29 is a performance plot when pairing QCOM8 TSC2 with legacy TSC2;

FIG. 30 is a performance plot when pairing QCOM8 TSC3 with legacy TSC3;

FIG. 31 is a performance plot when pairing QCOM8 TSC4 with legacy TSC4;

FIG. 32 is a performance plot when pairing QCOM8 TSC5 with legacy TSC5;

FIG. 33 is a performance plot when pairing QCOM8 TSC6 with legacy TSC6;and

FIG. 34 is a performance plot when pairing QCOM8 TSC7 with legacy TSC7;

FIG. 35 is a flowchart illustrating a method of transmitting two signalson a single channel comprising a single frequency and a single timeslot; and

FIG. 36 is a flowchart comprising steps taken to signal trainingsequence information to a remote station.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention can be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed without these specific details. In some instances, well knownstructures and devices are shown in block diagram form in order to avoidobscuring the concepts of the present invention.

Interference due to other users limits the performance of wirelessnetworks. This interference can take the form of either interferencefrom neighboring cells on the same frequency, known as CCI, discussedabove, or neighboring frequencies on the same cell, known as ACI, alsodiscussed above.

Single-antenna interference cancellation (SAIC) is used to reduceCo-Channel Interference (CCI), The 3G Partnership Project (3GPP) hasstandardized SAIC performance. SAIC is a method used to combatinterference. The 3GPP adopted the term downlink advanced receiverperformance (DARP) to describe a receiver that applies SAIC to achieveenhanced interference rejection capability.

DARP increases network capacity by employing lower reuse factors.Furthermore, it suppresses interference at the same time. DARP operatesat the baseband part of a receiver of a remote station. It suppressesadjacent-channel and co-channel interference that differ from generalnoise. DARP is available in previously defined GSM standards (sinceRel-6 in 2004) as a release-independent feature, and is an integral partof Rel-6 and later specs. The following is a description of two DARPmethods. The first is the joint detection/demodulation (JD) method. JDuses knowledge of the GSM signal structure in adjacent cells insynchronous mobile networks to demodulate one of several interferencesignals in addition to the desired signal. JD's ability to retrieveinterference signals allows the suppression of specific adjacent-channelinterferers. In addition to demodulating GMSK signals, JD also can beused to demodulate EDGE signals. Blind interferer cancellation (BIC) isanother method used in DARP to demodulate the GMSK signal. With BIC, thereceiver has no knowledge of the structure of any interfering signalsthat may be received at the same time that the desired signal isreceived. Since the receiver is effectively “blind” to anyadjacent-channel interferers, the method attempts to suppress theinterfering component as a whole. The GMSK signal is demodulated fromthe wanted carrier by the BIC method. BIC is most effective when usedfor GMSK-modulated speech and data services and can be used inasynchronous networks.

A DARP capable remote station equalizer/detector 426 of the presentmethod and apparatus also performs CCI cancellation prior toequalization, detection, etc. Equalizer/detector 426 in FIG. 2 providesdemodulated data. CCI cancellation normally is available on a BS. Also,remote stations may or may not be DARP capable. The network maydetermine whether a remote station is DARP capable or not at theresource assignment stage, a starting point of a call, for a GSM remotestation (e.g. mobile station).

It is desirable to increase the number of active connections to remotestations that can be handled by a base station. FIG. 5 of theaccompanying drawings shows a simplified representation of a cellularcommunications system 100. The system comprises base stations 110, 111and 114 and remote stations 123, 124, 125, 126 and 127. Base stationcontrollers 141 to 144 act to route signals to and from the differentremote stations 123-127, under the control of mobile switching centres151, 152. The mobile switching centres 151, 152 are connected to apublic switched telephone network (PSTN) 162. Although remote stations123-127 are commonly handheld mobile devices, many fixed wirelessdevices and wireless devices capable of handling data also fall underthe general title of remote station 123-127.

Signals carrying, for example, voice data are transferred between eachof the remote stations 123-127 and other remote stations 123-127 bymeans of the base station controllers 141-144 under the control of themobile switching centres 151, 152. Alternatively, signals carrying, forexample, voice data are transferred between each of the remote stations123-127 and other communications equipment of other communicationsnetworks via the public switched telephone network 162. The publicswitched telephone network 162 allows calls to be routed between themobile cellular system 100 and other communication systems. Such othersystems include other mobile cellular communications systems 100 ofdifferent types and conforming to different standards.

Each of remote stations 123-127 can be serviced by any one of a numberof base stations 110, 111, 114. A remote station 124 receives both asignal transmitted by the serving base station 114 and signalstransmitted by nearby non-serving base stations 110, 111 and intended toserve other remote stations 125.

The strengths of the different signals from base stations 110, 111, 114are periodically measured by the remote station 124 and reported to BSC144, 114, etc. If the signal from a nearby base station 110, 111 becomesstronger than that of the serving base station 114, then the mobileswitching centre 152 acts to make the nearby base station 110 become theserving base station and acts to make the serving base station 114become a non-serving base station and handovers the signal to the nearbybase station 110. Handover refers to the method of transferring a datasession or an ongoing call from one channel connected to the corenetwork to another.

In cellular mobile communications systems, radio resources are dividedinto a number of channels. Each active connection (for example a voicecall) is allocated a particular channel having a particular channelfrequency for the downlink signal (transmitted by the base station 110,111, 114 to a remote station 123-127 and received by the remote station123-127) and a channel having a particular channel frequency for theuplink signal (transmitted by the remote station 123-127 to the basestation 110, 111, 114 and received by the base station 110, 111, 114).The frequencies for downlink and uplink signals are often different, toallow simultaneous transmission and reception and to reduce interferencebetween transmitted signals and the received signals at the remotestation or 123-127 at the base station 110, 111, 114.

A method for cellular systems to provide access to many users isfrequency reuse. FIG. 6 of the accompanying drawings shows anarrangement of cells in a cellular communications system that usesfrequency reuse. This particular example has a reuse factor of 4:12,which represents 4 cells:12 frequencies. That means that the 12frequencies available for a base station are allocated to the basestation's four sites labeled A-D illustrated in FIG. 6. Each site isdivided into three sectors (or cells). Stated another way, one frequencyis allocated to each of the three sectors of each of 4 sites so that allof the 12 sectors (3 sectors/site for 4 sites) have differentfrequencies. The frequency reuse pattern repeats itself after the fourthcell. FIG. 6 illustrates the system's cell repeat pattern 210 wherebybase station 110 belongs to cell A, base station 114 belongs to cell B,base station 111 belongs to cell C and so on. Base station 110 has aservice area 220 that overlaps with adjacent service areas 230 and 240of adjacent base stations 111 and 114 respectively. Remote stations 124,125 are free to roam between the service areas. As discussed above, toreduce interference of signals between cells, each cell is allocated aset of channel frequencies, where each frequency may support one or morechannels, such that adjacent cells are allocated different sets ofchannel frequencies. However, two cells that are non-adjacent may usethe same set of frequencies. Base station 110 could use for examplefrequency allocation set A comprising frequencies f1, f2 and f3 forcommunicating with remote stations 125 in its service area 220.Similarly, base station 114 could use for example frequency allocationset B comprising frequencies f4, f5 and f6, to communicate with remotestations 124 in its service area 240, and so on. The area defined bybold border 250 contains one four-site repeat pattern. The repeatpattern repeats in a regular arrangement for the geographical areaserviced by the communications system 100. It may be appreciated thatalthough the present example repeats itself after 4 sites, a repeatpattern may have a number of sites other than four and a total number offrequencies other than 12.

As stated above with GSM, each carrier frequency is divided using TDMA.TDMA is a multiple access technique directed to providing increasedcapacity. Using TDMA, each carrier frequency is segmented into intervalscalled frames. Each frame is further partitioned into assignable usertime slots. In GSM, the frame is partitioned into eight time slots.Thus, eight consecutive time slots form one TDMA frame with a durationof 4.615 ms.

A physical channel occupies one time slot within each frame on aparticular frequency. The TDMA frames of a particular carrier frequencyare numbered, each user being assigned one or more time slots withineach frame. Furthermore, the frame structure repeats, so that a fixedTDMA assignment constitutes one or more slots that periodically appearduring each time frame. Thus, each base station can communicate with aplurality of remote stations 123-127 using different assigned time slotswithin a single channel frequency. As stated above, the time slotsrepeat periodically. For example, a first user may transmit on the1^(st) slot of every frame of frequency f1, while a second user maytransmit on the 2^(nd) slot of every frame of frequency f2. During eachdownlink time slot, the remote station 123-127 is given access toreceive a signal transmitted by the base station 110, 111, 114 andduring each uplink time slot the base station 110, 111, 114 is givenaccess to receive a signal transmitted by the remote station 123-127.The channel for communication to a mobile station 123-127 thus comprisesboth a frequency and a time slot, for a GSM system. Equally, the channelfor communication to a base station 110, 111, 114 comprises both afrequency and a time slot.

FIG. 7 shows an example arrangement of time slots for a time divisionmultiple access (TDMA) communications system. A base station 114transmits data signals in a sequence of numbered time slots 30, eachsignal being for only one of a set of remote stations 123-127 and eachsignal being received at the antenna of all remote stations 123-127within range of the transmitted signals. The base station 114 transmitsall the signals using slots on an allocated channel frequency. Forexample, a first remote station 124 might be allocated a first time slot3 and a second remote station 126 might be allocated a second time slot5. The base station 114 transmits, in this example, a signal for thefirst remote station 124 during time slot 3 of the sequence of timeslots 30, and transmits a signal for the second remote station 126during time slot 5 of the sequence of time slots 30.

The first and second remote stations 124, 126 are active during theirrespective time slots 3 and 5 of time slot sequence 30, to receive thesignals from the base station 114. The remote stations 124, 126 transmitsignals to the base station 114 during corresponding time slots 3 and 5of time slot sequence 31 on the uplink. It can be seen that the timeslots for the base station 114 to transmit (and the remote stations 124,126 to receive) 30 are offset in time with respect to the time slots forthe remote stations 124, 126 to transmit (and the base station 114 toreceive) 31.

This offsetting in time of transmit and receive time slots is known astime division duplexing (TDD), which among other things, allows transmitand receive operations to occur at different instances of time.

Voice data signals are not the only signals to be transmitted betweenthe base station 110, 111, 114 and the remote station 123-127. A controlchannel is used to transmit data that controls various aspects of thecommunication between the base station 110, 111, 114 and the remotestation 123-127.

Among other things, the base station 110, 111, 114 uses the controlchannel to send to the remote station 123-127 a sequence code, ortraining sequence code (TSC) which indicates which of a set of sequencesthe base station 110, 111, 114 will use to transmit the signal to theremote station 123-127. In GSM, a 26-bit training sequence is used forequalization. This is a known sequence which is transmitted in a signalin the middle of every time slot burst.

The sequences are used by the remote station 123-127: to compensate forchannel degradations which vary quickly with time; to reduceinterference from other sectors or cells; and to synchronize the remotestation's receiver to the received signal. These functions are performedby an equalizer which is part of the remote station's 123-127 receiver.An equalizer 426 determines how the known transmitted training sequencesignal is modified by multipath fading. Equalization may use thisinformation to extract the desired signal from the unwanted reflectionsby constructing an inverse filter to extract the rest of the desiredsignal. Different sequences (and associated sequence codes) aretransmitted by different base stations 110, 111, 114 in order to reduceinterference between sequences transmitted by base stations 110, 111,114 that are close to each other.

As stated above, with DARP the remote station 123-127 of the presentmethod and apparatus is able to use the sequence to distinguish thesignal transmitted to it by the base station 110, 111, 114 serving theremote station 123-127 from other unwanted signals transmitted bynon-serving base stations 110, 111, 114 of other cells. This holds trueso long as the received amplitudes or power levels of the unwantedsignals are below a threshold relative to the amplitude of the wantedsignal.

The unwanted signals can cause interference to the wanted signal if theyhave amplitudes above this threshold. In addition, the threshold canvary according to the capability of the remote station's 123-127receiver. The interfering signal and the desired (or wanted) signal canarrive at the remote station's 123-127 receiver contemporaneously if,for example, the signals from the serving and non-serving base stations110, 111, 114 share the same time slot for transmitting.

Referring again to FIG. 5, at remote station 124, transmissions frombase station 110 for remote station 125 can interfere with transmissionsfrom base station 114 for remote station 124 (the path of theinterfering signal shown by dashed arrow 170). Similarly, at remotestation 125 transmissions from base station 114 for remote station 124can interfere with transmissions from base station 110 for remotestation 125 (the path of the interfering signal shown by dotted arrow182).

TABLE 1

Table 1 shows example values of parameters for signals transmitted bythe two base stations 110 and 114 illustrated in FIG. 6. The informationin rows 3 and 4 of Table 1 show that for remote station 124 both awanted signal from a first base station 114 and an unwanted interferersignal from a second base station 110 and intended for remote station125 are received and the two received signals have the same channel andsimilar power levels (−82 dBm and −81 dBm respectively).

Similarly, the information in rows 6 and 7 show that for remote station125 both a wanted signal from the second base station 110 and anunwanted interferer signal from the first base station 114 and intendedfor remote station 124 are received and the two received signals havethe same channel and similar power levels (−80 dBm and −79 dBmrespectively).

Each remote station 124, 125 thus receives both a wanted signal and anunwanted interferer signal that have similar power levels from differentbase stations 114, 110, on the same channel (i.e. contemporaneously).Because the two signals arrive on the same channel and similar powerlevels, they interfere with each other. This may cause errors indemodulation and decoding of the wanted signal. This interference isco-channel interference discussed above.

The co-channel interference may be mitigated to a greater extent thanpreviously possible, by the use of DARP enabled remote stations 123-127,base stations 110, 111, 114 and base station controllers 151, 152. Whilebase stations 110, 111, 114 may be capable of simultaneously receivingand demodulating two co-channel signals having similar power levels,DARP allows remote stations 123-127 to have, by means of DARP, similarcapability. This DARP capability may be implemented by means of a methodknown as single antenna interference cancellation (SAIC) or by means ofa method known as dual antenna interference cancellation (DAIC).

The receiver of a DARP-capable remote station 123-127 may demodulate awanted signal while rejecting an unwanted co-channel signal even whenthe amplitude of the received unwanted co-channel signal is similar orhigher than the amplitude of the wanted signal. The DARP feature worksbetter when the amplitudes of the received co-channel signals aresimilar. This situation would typically occur in existing systems suchas GSM not yet employing the present method and apparatus, when each oftwo remote stations 123-127, each communicating with a different basestation 110, 111, 114, is near a cell boundary, where the path lossesfrom each base station 110, 111, 114 to each remote station 123-127 aresimilar.

A remote station 123-127 that is not DARP-capable, by contrast, may onlydemodulate the wanted signal if the unwanted co-channel interferersignal has an amplitude, or power level, lower than the amplitude of thewanted signal. In one example, it may be lower by at least 8 dB. TheDARP-capable remote station 123-127 can therefore tolerate a muchhigher-amplitude co-channel signal relative to the wanted signal, thancan the remote station 123-127 not having DARP capability.

The co-channel interference (CCI) ratio is the ratio between the powerlevels, or amplitudes, of the wanted and unwanted signals expressed indB. In one example, the co-channel interference ratio could be, forexample, −6 dB (whereby the power level of the wanted signal is 6 dBlower than the power level of the co-channel interferer (or unwanted)signal). In another example, the ratio may be +6 dB (whereby the powerlevel of the wanted signal is 6 dB higher than the power level of theco-channel interferer (or unwanted) signal). For those remote stations123-127 of the present method and apparatus with good DARP performance,the amplitude of the interferer signal can be as much as 10 dB higherthan the amplitude of the wanted signal, and the remote stations 123-127may still process the wanted signal. If the amplitude of the interferersignal is 10 dB higher than the amplitude of the wanted signal, theco-channel interference ratio is −10 dB.

DARP capability, as described above, improves a remote station's 123-127reception of signals in the presence of ACI or CCI. A new user, withDARP capability, will better reject the interference coming from anexisting user. The existing user, also with DARP capability, would dothe same and not be impacted by the new user. In one example, DARP workswell with CCI in the range of 0 dB (same level of co-channelinterference for the signals) to −6 dB (co-channel is 6 dB stronger thanthe desired or wanted signal). Thus, two users using the same ARFCN andsame timeslot, but assigned different TSCs, will get good service.

The DARP feature allows two remote stations 124 and 125, if they bothhave the DARP feature enabled, to each receive wanted signals from twobase stations 110 and 114, the wanted signals having similar powerlevels, and each remote station 124, 125 to demodulate its wantedsignal. Thus, the DARP enabled remote stations 124, 125 are both able touse the same channel simultaneously for data or voice.

The feature described above of using a single channel to support twosimultaneous calls from two base stations 110, 111, 114 to two remotestations 123-127 is somewhat limited in its application. To use thefeature, the two remote stations 124, 125 are within range of the twobase stations 114, 110 and are each receiving the two signals at similarpower levels. For this condition, typically the two remote stations 124,125 would be near the cell boundary, as mentioned above.

The present method and apparatus allows the supporting of two or moresimultaneous calls on the same channel (consisting of a time slot on acarrier frequency), each call comprising communication between a singlebase station 110, 111, 114 and one of a plurality of remote stations123-127 by means of a signal transmitted by the base station 110, 111,114 and a signal transmitted by the remote station 123-127. The presentmethod and apparatus provides a new and inventive application for DARP.As stated above, with DARP, two signals on the same time slot on thesame carrier frequency may be distinguished by using different trainingsequences at higher levels of interference than was possible before DARPwas available for use. Since the signal from the BS 110, 111, 114 notbeing used by the remote station (i.e. the unwanted signal) acts asinterference, DARP acts to filter/suppress the unwanted signal by use ofthe training sequences.

The present method and apparatus allows the use of two or more trainingsequences in the same cell. In the prior art, one of the trainingsequences, the one not assigned to the base station 110, 111, 114, willonly act as interference as it also does in Multi-User on One Slot(MUROS) for at least one mobile station's 123-127 receiver. However, akey difference is that the unwanted signal for that mobile station iswanted by another mobile station 123-127 in the same cell. In legacysystems, the unwanted signal is for a mobile station 123-127 in anothercell, not the same cell.

According to the present method and apparatus, both training sequencesignals may be used in the same time slot on the same carrier frequencyin the same cell by the same base station 110, 111, 114. Since twotraining sequences can be used in a cell, twice as many communicationchannels may be used in the cell. By taking a training sequence whichwould normally be interference from another (non-neighboring) cell orsector and allowing a base station 110, 111, 114 to use it in additionto its already-used training sequence, the number of communicationchannels is doubled.

DARP, when used along with the present method and apparatus, thereforeenables a GSM network to use a co-channel already in use (i.e., theARFCN that is already in use) to serve additional users. In one example,each ARFCN can be used for two users for full-rate (FR) speech and 4 forhalf-rate (HR) speech. It is also possible to serve the third or evenfourth user if the MSs have excellent DARP performance. In order toserve additional users using the same AFRCN on the same timeslot, thenetwork transmits the additional users' RF signal on the same carrier,using a different phase shift, and assigns the same traffic channel (thesame ARFCN and timeslot that is in use) to the additional user using adifferent TSC. The bursts are modulated with the training sequencecorresponding to the TSC accordingly. A DARP capable remote station maydetect the wanted or desired signal. It is possible to add the third andfourth users in the same way as the first and second users were.

FIG. 8A of the accompanying drawings shows an apparatus for operating ina multiple access communication system to produce first and secondsignals sharing a single channel. A first data source 401 and a seconddata source 402 (for a first and a second remote station 123-127)produce first data 424 and second data 425 for transmission. A sequencegenerator 403 generates a first sequence 404 and a second sequence 405.A first combiner 406 combines the first sequence 404 with the first 424data to produce first combined data 408. A second combiner 407 combinesthe second sequence 405 with the second data 425 to produce secondcombined data 409.

The first and second combined data 408, 409 are input to a transmittermodulator 410 for modulating both the first and the second combined data408, 409 using a first carrier frequency 411 and a first time slot 412.In this example, the carrier frequency may generated by an oscillator421. The transmitter modulator outputs a first modulated signal 413 anda second modulated signal 414 to a RF front end 415. The RF front endprocesses the first and second modulated signals 413, 414 byupconverting them from baseband to an RF (radio frequency) frequency.The upconverted signals are sent to antennas 416 and 417 where they arerespectively transmitted.

The first and second modulated signals may be combined in a combinerprior to being transmitted. The combiner 422 may be a part of either thetransmitter modulator 410 or the RF front end 415 or a separate device.A single antenna 416 provides means for transmitting the combined firstand second signals by radiation. This is illustrated in FIG. 8B.

FIG. 9 of the accompanying drawings shows a method for using theapparatuses for operating in a multiple access communication system toproduce first and second signals sharing a single channel shown in FIGS.8A and 8B. The method includes allocating a particular channel frequencyand a particular time slot for a base station 110, 111, 114 to use totransmit to a plurality of remote stations 123-127 whereby a differenttraining sequence is assigned for each remote station 123-127. Thus inone example, this method may be executed in the base station controller151, 152. In another example, this method may be executed in a basestation 110, 111, 114.

Following the start of the method 501, a decision is made in step 502 asto whether to set up a new connection between the base station 110, 111,114 and a remote station 123-127. If the answer is NO, then the methodmoves back to the start block 501 and the steps above are repeated. Whenthe answer is YES, a new connection is set up. Then in block 503 adecision is made as to whether there is an unused channel (i.e. anunused time slot for any channel frequency). If there is an unused timeslot on a used or unused channel frequency, then a new time slot isallocated in block 504. The method then moves back to the start block501 and the steps above are repeated.

When eventually there is no longer an unused time slot (because all timeslots are used for connections), the answer to the question of block 503is NO, and the method moves to block 505. In block 505, a used time slotis selected for the new connection to share with an existing connection,according to a set of first criteria. There can be a variety ofcriteria. For example one criterion might be that a time slot may beselected if it has low traffic. Another criterion may be that the timeslot is already used by no more than one remote station 123-127. It canbe appreciated that there will be other possible criteria based on thenetwork planning methods employed, and the criteria is not limited tothose two examples.

A used time slot on a channel frequency having been selected for the newconnection to share along with an existing connection, a TSC for the newconnection is then selected in block 506 according to a set of secondcriteria. These second criteria may include some of the criteria usedfor the selection of the time slot in block 505, or other criteria. Onecriterion is that the TSC has not yet been used by the cell or sectorfor the channel comprising the used time slot. Another criterion mightbe that the TSC is not used on that channel by a nearby cell or sector.The method then moves back to the start block 501 and the steps aboveare repeated.

FIG. 10A of the accompanying drawings shows an example wherein themethod described by FIG. 9 would reside in the base station controller600. Within base station controller 600 reside controller processor 660and memory subsystem 650. The steps of the method may be stored insoftware 680 in memory 685 in memory subsystem 650, or within software680 in memory 685 residing in controller processor 660, or withinsoftware 680 memory 685 in the base station controller 600, or withinsome other digital signal processor (DSP) or in other forms of hardware.The base station controller 600 is connected to the mobile switchingcentre 610 and also to base stations 620, 630 and 640, as shown by FIG.10A.

Shown within memory subsystem 650 are parts of three tables of data 651,652, 653. Each table of data stores values of a parameter for a set ofremote stations 123, 124 indicated by the column labeled MS. Table 651stores values of training sequence code. Table 652 stores values fortime slot number TS. Table 653 stores values of channel frequency CHF.It can be appreciated that the tables of data could alternatively bearranged as a multi-dimensional single table or several tables ofdifferent dimensions to those shown in FIG. 10A.

Controller processor 660 communicates via data bus 670 with memorysubsystem 650 in order to send and receive values for parameters to/frommemory subsystem 650. Within controller processor 660 are containedfunctions that include a function 661 to generate an access grantcommand, a function 662 to send an access grant command to a basestation 620, 630, 640, a function 663 to generate a traffic assignmentmessage, and a function 664 to send a traffic assignment message to abase station 620, 630 or 640. These functions may be executed usingsoftware 680 stored in memory 685.

Within controller processor 660, or elsewhere in the base stationcontroller 600, there may also be a power control function 665 tocontrol the power level of a signal transmitted by a base station 620,630 or 640.

It can be appreciated that the functions shown as being within basestation controller 600, namely memory subsystem 650 and controllerprocessor 660 could also reside in the mobile switching centre 610.Equally some or all of the functions described as being part of basestation controller 600 could equally well reside in one or more of basestations 620, 630 or 640.

FIG. 10B is a flowchart disclosing the steps executed by the basestation controller 600. When allocating a channel to a remote station123, 124 (e.g. remote station MS 23), for example when the remotestation 123 requests service, the base station 620, 630, 640 wishing toservice the remote station 123, 124 sends a request message to the basestation controller 600 for a channel assignment.

Controller processor 660, upon receiving the request message at step 602via data bus 670, determines if a new connection is required. If theanswer is NO, then the method moves back to the start block 601 and thesteps above are repeated. When the answer is YES a new connection set upis initiated. Then in block 603 a decision is made as to whether thereis an unused channel (i.e. an unused time slot for any channelfrequency). If there is an unused time slot on a used or unused channelfrequency, then a new time slot is allocated in block 604. The methodthen moves back to the start block 601 and the steps above are repeated.

On the other hand, if the controller processor 660 determines there isnot an unused time slot on any channel frequency, it selects a used timeslot. See step 605 of FIG. 10B. The selection could be based onaccessing memory subsystem 650 or other memory 685 to obtain informationon criteria such as the current usage of time slots, and whether both oronly one of remote stations 123, 124 are DARP enabled.

Controller processor 660 selects a used time slot, and selects atraining sequence code for the time slot. See step 606 of FIG. 10B Sincethe time slot is already used, this will be the second training sequenceselected for that time slot.

In order to apply criteria for selecting a time slot, the controllerprocessor 660 accesses memory 650 via data bus 670, or accesses othermemory 685, to obtain information, for example information about thecurrent allocation of time slots or training sequences or both, andwhether remote stations 123, 124 have DARP capability. Controllerprocessor 660 then generates a command (661 or 663) and sends thecommand (662 or 664) to the base station 620 to assign a channelfrequency, time slot and training sequence to the remote station 123.The method then moves back to the start block 601 and the steps aboveare repeated.

FIG. 11 of the accompanying drawings shows the flow of signals in a basestation 620, 920. Base station controller interface 921 communicates,via communications link 950, with a base station controller 600.Communications link 950 might be a data cable or a RF link for example.Controller processor 960 communicates with and controls, via data bus970, receiver components 922, 923 and 924, and transmitter components927, 928, and 929. Controller processor 960 communicates via data bus980 with BSC interface 921. The data bus 970 could comprise just one busor several buses and could be partly or wholly bi-directional. Databuses 970 and 980 could be the same bus.

In one example, a message requesting grant of a channel is received froma remote station 123, 124 in a coded, modulated, radiated signal at basestation antenna 925 and is input to duplexer switch 926. The signalpasses from the receive port of duplexer switch 926 to the receiverfront end 924 which conditions the signal (for example by means ofdown-converting, filtering, and amplifying). The receiver demodulator923 demodulates the conditioned signal and outputs the demodulatedsignal to channel decoder and de-interleaver 922 which decodes andde-interleaves the demodulated signal and outputs the resulting data tocontroller processor 960.

Controller processor 960 derives from the resulting data the messagerequesting grant of a channel. Controller processor 960 sends themessage via base station controller interface 921 to a base stationcontroller 600. The base station controller 600 then acts to grant, ornot grant, a channel to the remote station 23, 24, either autonomouslyor together with mobile switching centre 610.

Base station controller 600 generates and sends access grant commands,and other digital communication signals or traffic for remote stations123, 124, for example assignment messages, to BSC interface 921 viacommunications link 950. The signals are then sent via data bus 980 tocontroller processor 960. Controller processor 960 outputs signals forremote stations 123, 124 to coder and interleaver 929 and the coded andinterleaved signals then pass to transmitter modulator 928. It can beseen from FIG. 11 that there are several signals input to transmittermodulator 928, each signal for a remote station 123, 124. These severalsignals can be combined within transmitter modulator 928 to provide acombined modulated signal having I and Q components as shown in FIG. 11.However the combining of the several signals could alternatively beperformed post-modulation within transmitter front end module 927 and orin other stages within the transmit chain. The modulated combined signalis output from transmitter front end 927 and input to the transmit portof duplexer switch 926. The signal is then output via the common orantenna port of duplexer switch 926 to the antenna 925 for transmission.

In another example, a second message from a second remote station 123,124 requesting grant of a channel is received in a second receivedsignal at the base station antenna 925. The second received signal isprocessed as described above and the request for grant of a channel issent in the processed second received signal to the base stationcontroller 600.

The base station controller 600 generates and sends to the base station620, 920 a second access grant message as described above, and the basestation 620, 920 transmits a signal comprising the second access grantmessage, as described above, for the remote station 123, 124.

FIG. 12 of the accompanying drawings shows example arrangements for datastorage within a memory subsystem 650 which might reside within a basestation controller (BSC) 600 of the present method and apparatus ofcellular communication system 100. Table 1001 of FIG. 12 is a table ofvalues of channel frequencies assigned to remote stations 123-127, theremote stations 123-127 being numbered. Table 1002 is a table of valuesof time slots wherein remote station numbers 123-127 are shown againsttime slot number. It can be seen that time slot number 3 is assigned toremote stations 123, 124 and 229. Similarly table 1003 shows a table ofdata allocating training sequences (TSCs) to remote stations 123-127.

Table 1005 of FIG. 12 shows an enlarged table of data which ismulti-dimensional to include all of the parameters shown in tables 1001,1002, and 1003 just described. It will be appreciated that the portionof table 1005 shown in FIG. 12 is only a small part of the completetable that would be used. Table 1005 shows in addition the allocation offrequency allocation sets, each frequency allocation set correspondingto a set of frequencies used in a particular sector of a cell or in acell. In Table 1005, frequency allocation set f1 is assigned to allremote stations 123-127 shown in the table 1005 of FIG. 12. It will beappreciated that other portions of Table 1005, which are not shown, willshow frequency allocation sets f2, f3 etc. assigned to other remotestations 123-127. The fourth row of data shows no values but repeateddots indicating that there are many possible values not shown betweenrows 3 and 5 of the data in table 1001.

Phase Shift

The absolute phase of the modulation for the two signals transmitted bythe base station 110, 111, 114 may not be identical. In order to serveadditional users using the same channel (co-TCH), in addition toproviding more than one TSC, the network may phase shift the symbols ofthe RF signal of the new co-channel (co-TCH) remote station with respectto the existing co-TCH remote station(s). If possible the network maycontrol them with evenly distributed spaced phase shift, thus improvingreceiver performance.

For example, the phase shift of the carrier frequency (having aparticular ARFCN) for two users would be 90 degrees apart, three users60 degrees apart. The phase shift of the carrier (ARFCN) for four userswould be 45 degree apart. As stated above, the users will use differentTSCs. Each additional remote station 123-127 of the present method andapparatus is assigned a different TSC and uses its own TSC and the DARPfeature to get its own traffic data.

Thus, for improved DARP performance, the two signals intended for thetwo different mobile stations (remote stations) 123, 124 may ideally bephase shifted by π/2 for their channel impulse response, but less thanthis will also provide adequate performance.

When the first and second remote stations 123, 124 are assigned the samechannel (i.e. same time slot on the same channel frequency), signals maypreferably be transmitted to the two remote stations 123, 124 (usingdifferent training sequences as described previously) such that themodulator 928 modulates the two signals at 90 degrees phase shift toeach other, thus further reducing interference between the signals dueto phase diversity. So, for example, the I and Q samples emerging fromthe modulator 928 could each represent one of the two signals, thesignals being separated by 90 degrees phase. The modulator 928 thusintroduces a phase difference between the signals for the two remotestations 123, 124.

In the case of several remote stations 123, 124 sharing the samechannel, multiple sets of I and Q samples can be generated withdifferent offsets. For example, if there is a third signal for a thirdremote station 123, 124 on the same channel, the modulator 928introduces phase shifts of preferably 60 degrees and 120 degrees for thesecond and third signals relative to the phase of the first signal, andthe resulting I and Q samples represent all three signals. For example,the I and Q samples could represent the vector sum of the three signals.

In this way, the transmitter modulator 928 provides means at the basestation 620, 920 for introducing a phase difference betweencontemporaneous signals using the same time slot on the same frequencyand intended for different remote stations 123, 124. Such means can beprovided in other ways. For example, separate signals can be generatedin the modulator 928 and resulting analogue signals can be combined inthe transmitter front end 927 by passing one of them through a phaseshift element and then simply summing the phase shifted and non-phaseshifted signals.

Power Control Aspects

Table 2 below shows example values of channel frequency, time slot,training sequence and received signal power level for signalstransmitted by the two base stations 110 and 114 as shown in FIG. 5 andreceived by remote stations 123 to 127.

TABLE 2

The rows 3 and 4 of Table 2, outlined by a bold rectangle, show bothremote station 123 and remote station 124 using a channel frequencyhaving index 32 and using time slot 3 for receiving a signal from basestation 114 but allocated different training sequence codes TSC2 andTSC3 respectively. Similarly, rows 9 and 10 also show the same channelfrequency and time slot being used for two remote stations 125, 127 toreceive signals from the same base station 110. It can be seen that ineach case the remote station 125, 127 received power levels of thewanted signals are substantially different for the two remote stations125, 127.

The highlighted rows 3 and 4 of Table 3 show that base station 114transmits a signal for remote station 123 and also transmits a signalfor remote station 124. The received power level at remote station 123is −67 dBm whereas the received power level at remote station 124 is−102 dBm. Rows 9 and 10 of Table 3 show that base station 110 transmitsa signal for remote station 125 and also transmits a signal for remotestation 127. The received power level at remote station 125 is −101 dBmwhereas the received power level at remote station 127 is −57 dBm. Thelarge difference in power level, in each case, could be due to differentdistances of the remote stations 125, 127 from the base station 110.Alternatively the difference in power levels could be due to differentpath losses or different amounts of multi-path cancellation of thesignals, between the base station transmitting the signals and theremote station receiving the signals, for one remote station as comparedto the other remote station.

Although this difference in received power level for one remote stationcompared to the other remote station is not intentional and not idealfor cell planning, it does not compromise the operation of the presentmethod and apparatus.

A remote station 123-127 having DARP capability may successfullydemodulate either one of two co-channel, contemporaneously receivedsignals, so long as the amplitudes or power levels of the two signalsare similar at the remote station's 123-127 antenna. This is achievableif the signals are both transmitted by the same base station 110, 111,114 and (could have more than one antenna, e.g., one per signal) thepower levels of the two transmitted signals are substantially the samebecause then each remote station 123-127 receives the two signals atsubstantially the same power level (say within 6 dB of each other). Thetransmitted powers are similar if either the base station 110, 111, 114is arranged to transmit the two signals at similar power levels, or thebase station 110, 111, 114 transmits both signals at a fixed powerlevel. This situation can be illustrated by further reference to Table 2and by reference Table 3.

While Table 2 shows remote stations 123, 124 receiving from base station114 signals having substantially different power levels, on closerinspection it can be seen that, as shown by rows 3 and 5 of Table 2,remote station 123 receives two signals from base station 114 at thesame power level (−67 dBm), one signal being a wanted signal intendedfor remote station 123 and the other signal being an unwanted signalwhich is intended for remote station 124. The criteria for a remotestation 123-127 to receive signals having similar power levels is thusshown as being met in this example. If mobile station 123 has a DARPreceiver, it can, in this example, therefore demodulate the wantedsignal and reject the unwanted signal.

Similarly, it can be seen by inspecting rows 4 and 6 of Table 2 (above)that remote station 124 receives two signals sharing the same channeland having the same power level (−102 dBm). Both signals are from basestation 114. One of the two signals is the wanted signal, for remotestation 124 and the other signal is the unwanted signal which isintended for use by remote station 123.

To further illustrate the above concepts, Table 3 is an altered versionof Table 2 wherein the rows of Table 2 are simply re-ordered. It can beseen that remote stations 123 and 124 each receive from one base station114 two signals, a wanted and an unwanted signal, having the samechannel and similar power levels. Also, remote station 125 receives fromtwo different base stations 110, 114 two signals, a wanted and anunwanted signal, having the same channel and similar power levels.

TABLE 3

The apparatus and method described above have been simulated and themethod has been found to work well in a GSM system. The apparatusdescribed above and shown in FIGS. 8A, 8B, 10A, 11 and 12 could be partof a base station 110, 111, 114 of a GSM system for example.

According to another aspect of the present method and apparatus it ispossible for a base station 110, 111, 114 to maintain a call with tworemote stations 123-127 using the same channel, such that a first remotestation 123-127 has a DARP-enabled receiver and a second remote station123-127 does not have a DARP-enabled receiver. The amplitudes of signalsreceived by the two remote stations 124-127 are arranged to be differentby an amount which is within a range of values, in one example it may bebetween 8 dB and 10 dB, and also arranged such that the amplitude of thesignal intended for the DARP-enabled remote station is lower than theamplitude of the signal intended for the non-DARP-enabled remote station124-127.

A MUROS or non-MUROS mobile may treat its unwanted signal asinterference. However, for MUROS, both signals may be treated as wantedsignals in a cell. An advantage with MUROS enabled networks (e.g., BSand BSC) is that the BS 110, 111, 114 may use two or more trainingsequences per timeslot instead of only one so that both signals may betreated as desired signals. The BS 110, 111, 114 transmits the signalsat suitable amplitudes so that each mobile of the present method andapparatus receives its own signal at a high enough amplitude and the twosignals maintain an amplitude ratio such that the two signalscorresponding to the two training sequences may be detected.

This feature may be implemented using software stored in memory in theBS 110, 111, 114 or BSC 600. For example, MSs 123-127 are selected forpairing based on their path losses and based on existing traffic channelavailability. However, MUROS can still work if the path losses are verydifferent for one mobile than for the other mobile 123-127. This mayoccur when one mobile 123-127 is much further away from the BS 110, 111,114.

Regarding power control there are different possible combinations ofpairings. Both MSs 123-127 can be DARP capable or only one DARP capable.In both cases, the received amplitudes or power levels at the mobiles123-127 may be within 10 dB of each other and the same goes for MS 2.However if only one remote station is DARP capable, a further constraintis that the non-DARP mobile 123-127 has its wanted (or desired) firstsignal higher than the second signal (in one example, at least 8 dBhigher than the second signal). The DARP capable mobile 123-127 receivesits second signal no more than a lower threshold below the first signal(in one example, it is no lower than 10 dB). Hence in one example, theamplitude ratio can be 0 dB to ±10 dB for DARP/DARP capable remotestations 123-127 or an 8 dB to 10 dB higher signal for non-DARP/DARP infavour of the non-DARP mobile. Also, it is preferable for the BS 110,111, 114 to transmit the two signals so that each remote station 123-127receives its wanted signal above its sensitivity limit. (In one example,it is at least 6 dB above its sensitivity limit). So if one remotestation 123-127 has more path loss, the BS 110, 111, 114 transmits thatremote station's signal at an amplitude appropriate to achieve this.This sets the absolute amplitude. The difference from the other signalthen determines the absolute amplitude of that other signal.

FIG. 13 of the accompanying drawings shows an example receiverarchitecture for a remote station 123-127 of the present method andapparatus having the DARP feature. In one example, the receiver isadapted to use either the single antenna interference cancellation(SAIC) equalizer 1105, or the maximum likelihood sequence estimator(MLSE) equalizer 1106. Other equalizers implementing other protocols mayalso be used. The SAIC equalizer is preferred for use when two signalshaving similar amplitudes are received. The MLSE equalizer is typicallyused when the amplitudes of the received signals are not similar, forexample when the wanted signal has an amplitude much greater than thatof an unwanted co-channel signal.

FIG. 14 of the accompanying drawings shows a simplified representationof part of a GSM system adapted to assign the same channel to two remotestations 123-127. The system comprises a base station transceiversubsystem (BTS), which is part of a base station 110, and two remotestations, mobile stations 125 and 127. The network can assign, via thebase station transceiver subsystem 110, the same channel frequency andthe same time slot to the two remote stations 125 and 127. The networkallocates different training sequences to the two remote stations 125and 127. Remote stations 125 and 127 are both mobile stations and areboth assigned a channel frequency having ARFCN equal to 160 and a timeslot with time slot index number, TS, equal to 3. Remote station 125 isassigned training sequence code (TSC) of 5 whereas 127 is assignedtraining sequence code (TSC) of 0. Each remote station 125, 127 willreceive its own signal (shown by solid lines in the figure) togetherwith the signal intended for the other remote station 125, 127 (shown bydotted lines in the figure). Each remote station 125, 127 is able todemodulate its own signal whilst rejecting the unwanted signal.

As described above, according to the present method and apparatus asingle base station 110, 111, 114 can transmit a first and secondsignal, the signals for first and second remote stations 123-127respectively, each signal transmitted on the same channel, and eachsignal having a different training sequence. The first remote station123-127 having DARP capability is able to use the training sequences todistinguish the first signal from the second signal and to demodulateand use the first signal, when the amplitudes of the first and secondsignals are substantially within, say, 10 dB of each other.

In summary, FIG. 14 shows that the network assigns the same physicalresources to two mobile stations, but allocates different trainingsequences to them. Each mobile will receive its own signal (shown as asolid line in FIG. 14) and that intended for the other co-TCH user(shown as a dotted line in FIG. 14). On the downlink, each mobilestation will consider the signal intended for the other mobile stationas a CCI and reject the interference. Thus, two different trainingsequences may be used to suppress the interference from another MUROSuser.

Pairing of Remote Stations

According to how the present method and apparatus is implemented, it maybe useful to identify which of the remote stations connected to aparticular BS are MUROS-capable without replying on radio accesscapability of MUROS classmark (as it is desirable to pair with legacy UEwith MUROS UE). It is possible that the BS could identify an remotestation's DARP capability by requesting the remote station's classmark.A classmark is a declaration from a remote station to a BS of itscapabilities. This is described in 24.008 of TS10.5.1.5-7 in the GERANstandards. Currently, the standards define a classmark indicative of aremote station's DARP capability but so far, no MUROS classmark orsupporting of new training sequence classmark has been defined.Therefore, it is not possible to identify whether or not a remotestation is MUROS capable using the classmark for a legacy remotestation. Additionally, despite the definition of a DARP classmark in thestandards, the standards do not require the remote station to send theclassmark to the BS to inform the BS of its capabilities. In fact, manymanufacturers do not design their DARP-capable remote stations to sendthe DARP classmark to the BS on call setup procedures for fear thattheir remote stations will automatically be assigned to noisier channelsby the BS, thereby potentially degrading the communication from thatremote station. It is therefore currently not possible to identify withany certainty, whether a remote station is MUROS-capable or evenDARP-capable. It is desirable to let legacy remote station to play apart in MUROS operation, as they do have the capability to doing that.The current issue is that there is no signaling to support that.

In theory, it would be possible for a BS to identify MUROS-capability ina remote station based on the International Mobile Equipment Identity(IMEI) of the remote station. The BS can establish the remote station'sIMEI by requesting it directly from the remote station. The IMEI isunique to the remote station and can be used to reference a databaselocated anywhere in the network, thereby identifying the model of mobilephone to which the remote station belongs, and additionally itscapabilities such as DARP and MUROS. If the phone is DARP or MUROScapable, it will be considered by the BS as a candidate for sharing aslot with another suitable remote station. However, while using the IMEIis theoretically possible, DARP or MUROS capability alone is not asufficient criterion for determining whether a particular remote stationcan share a TDMA slot with another remote station. In operation, the BSwill build up a list of remote stations currently connected to that BSwhich are DARP or MUROS capable. The identification of remote stationsable to share a particular slot considers other criteria.

Firstly, the interference rejection ability of the remote station in agiven noisy environment could be established. (See step 1610 offlowchart in FIG. 35). This knowledge is used to allocate the remotestation to the most suitable available shared slot. (See step 1620 offlowchart in FIG. 35). It is also used to permit the best pairing withother candidate remote stations. (See step 1630 of flowchart in FIG.35). One way of determining the interference rejection capability of anremote station is to send a ‘discovery burst’. This is a short radioburst in which a signal desired to be received by the remote station hasa known interference pattern superimposed on it. The discovery burstcontains a basic speech signal with a superimposed CCI signal atcontrolled power levels. When sending the discovery burst, a differenttraining sequence to the one being used for the call currently inoperation is sent. This distinguishes the discovery burst from theactual voice signal.

In a particular implementation of the present method and apparatus, theBit Error Probability (BEP) is measured. (Other parameters indicatingability of the remote station to reject interference may also be used asdiscussed below). This is sent in the remote station's periodic reportback to the BS. In the GERAN standards, the BEP is represented by thevalues 0-31 with 0 corresponding to a probability of bit error of 25%and 31 corresponding to a probability of 0.025%. In other words, thehigher the BEP, the greater the ability of the remote station to rejectinterference. The BEP is reported as part of an “enhanced measurementreport.” Once the burst has been sent, if the BEP of the remote stationfalls below a given threshold, in the following report, the remotestation is considered to be unsuitable for MUROS operations. Insimulations, a BEP of at least 25 has been shown to be an advantageouschoice of threshold. It is of note that the BEP is derived by sending aburst over the channel and measuring the number of errors occurring inthe burst at the remote station. However, the BEP on its own may not bean accurate enough measure of the qualities of the remote station andthe channel, particularly if there is a dramatic variation of errorfrequency across the burst. It may therefore be preferable to base theMUROS operation decision on the mean BEP taking account of theco-variance of the BEP (CVBEP). These two quantities are mandated by thestandards as being present in the report the remote station sends to theBS.

Alternatively, the decision could be based on the RxQual parameterreturned to the BS by the remote station for one SACCH period (0.48 ms).RxQual is a value between 0-7 where each value corresponds to anestimated number of bit errors in a number of bursts (see 3GPP TS05.08).This is a standards defined measurement of reception quality consistingof eight levels and corresponds to the Bit Error Rate (BER) of thereceived signal. The higher the error rate, the higher RxQual.Simulations have shown an RxQual of 2 or lower to be an advantageouschoice of threshold for MUROS operation.

Alternatively, the parameter RxLev may equally be used as a selectioncriteria. RXLEV indicates the average signal strength received in dBm.This would also be reported to the remote station after the discoveryburst. An RxLev of at least 100 dBm has been shown to be advantageous.While particular criteria for MUROS pairing have been described, itwould be plain to the skilled person that many other criteria could beused instead or in combination with those identified above.

Joint Detection on the Uplink

The present method and apparatus uses GMSK and the DARP capability ofthe handset to avoid the need for the network to support a newmodulation method. A network may use existing methods on the uplink toseparate each user, e.g., joint detection. It uses co-channel assignmentwhere the same physical resources are assigned to two different mobiles,but each mobile is assigned a different training sequence. On the uplinkeach mobile station 123-127 of the present method and apparatus may usea different training sequence. The network may use a joint detectionmethod to separate two users on the uplink.

Speech Codec and Distance to New User

To reduce the interference to other cells, the BS 110, 111, 114 controlsits downlink power relative to the remote or mobile station's distancefrom it. When the remote station 123-127 is close to the BS 110, 111,114, the RF power level transmitted by the BS 110, 111, 114 to theremote station 123-127 on the downlink may be lower than to remotestations 123-127 that are further away from the BS 110, 111, 114. Thepower levels for the co-channel users are large enough for the callerwho is further away when they share the same ARFCN and timeslot. Theycan both have the same level of the power, but this can be improved ifthe network considers the distance of co-channel users from the basestation 110, 111, 114. In one example, power may be controlled byidentifying the distance and estimate the downlink power needed for thenew user 123-127. This can be done through the timing advance (TA)parameter of each user 123-127. Each user's 123-127 RACH provides thisinfo to the BS 110, 111, 114.

Similar Distances for Users

Another novel feature is to pick a new user with a similar distance as acurrent/existing user. The network may identify the traffic channel(TCH=ARFCN and TS) of an existing user who is in the same cell and atsimilar distance and needs roughly the same power level identifiedabove. Also, another novel feature is that the network may then assignthis TCH to the new user with a different TSC from the existing user ofthe TCH.

Selection of Speech Codec

Another consideration is that the CCI rejection of a DARP capable mobilewill vary depending on which speech codec is used. Thus, the network(NW) may use this criteria and assign different downlink power levelsaccording to the distance to the remote station 123-127 and the codecsused. Thus, it may be better if the network finds co-channel users whoare of similar distance to the BS 110, 111, 114. This is due to theperformance limitation of CCI rejection. If one signal is too strongcompared to the other, the weaker signal may not be detected due to theinterference. Therefore, the network may consider the distance from theBS 110, 111, 114 to new users when assigning co-channels andco-timeslots. The following are procedures which the network may executeto minimize the interference to other cells:

Frequency Hopping to Achieve User Diversity and Take Full Advantage ofDTx

Voice calls can be transmitted according to a DTx (discontinuoustransmission) mode. This is the mode of operation whereby the allocatedTCH burst can be quiet for the duration of no speech (while a user islistening to speech spoken by another user). The benefit of every TCH inthe cell using DTx is to reduce the overall power level of the servingcell on both UL and DL, hence the interference to other users can bereduced. This has significant effect, as normally people do have 40% oftime listening. The DTx feature can be used in MUROS mode as well toachieve the know benefit as stated.

There is an extra benefit for MUROS to be achieved when frequencyhopping is used to establish user diversity. When two MUROS users pairtogether, there could be some period of time both MUROS paired users arein DTx mode. Although this is a benefit to other cells as stated above,neither of the MUROS paired users get the benefit from sharing achannel. For this reason, when both are in DTx, the allocated resourcesare wasted. To take the advantage of this potentially helpful DTxperiod, one can let frequency hopping to take place so that a group ofusers are pairing with each other dynamically on every frame basis. Thismethod introduces user diversity into the MUROS operation, and reducesthe probability that both paired MUROS users are in DTx. It alsoincreases the probability of having one GMSK on the TCH. Benefitsinclude increasing the performance of speech calls and maximizing theoverall capacity of the NW.

An example of such case can be illustrated: Suppose the NW identified 8MUROS callers using full rate speech codecs, A, B, C, D, T, U, V, W, whouse similar RF power. Callers A, B, C, D can be non-frequency hopping.In addition, callers A, B, C, D are on the same timeslot, say TS3, butuse four different frequencies, ARFCN f1, f2, f3 and f4. Callers T, U,V, W are frequency hopping. In addition, callers T, U, V, W are on thesame timeslot TS3 and use frequencies f1, f2, f3 and f4 (MA list).Suppose they are given HSN=0, and MAIO 0, 1, 2 and 3 respectively. Thiswill let A, B, C, D pair with T, U, V, W in a cyclic form as shown inthe table below.

Frame No. 0 1 2 3 4 5 6 7 8 9 10 11 f1 A/T A/W A/V A/U A/T A/W A/V A/UA/T A/W A/V A/U f2 B/U B/T B/W B/V B/U B/T B/W B/V B/U B/T B/W B/V f3C/V C/U C/T C/W C/V C/U C/T C/W C/V C/U C/T C/W f4 D/W D/V D/U D/T D/WD/V D/U D/T D/W D/V D/U D/T

The above is only an example. This arrangement is selected to show howit works. However it should not be limited to this particulararrangement. It works even better if more randomness of pairing isintroduced. This can be achieved by putting all of 8 users on frequencyhopping on the four MA list, and give them different HSNs (in the aboveexample 0 to 3) and MAIOs, provided two users are each ARFCN.

Data Transfer

The first method pairs the traffic channel (TCH) being used. In oneexample, this feature is implemented on the network side, with minor orno changes made on the remote station side 123-127. The networkallocates a TCH to a second remote station 123-127 that is already inuse by a first remote station 123-127 with a different TSC. For example,when all the TCHs have been used, any additional service(s) requiredwill be paired with the existing TCH(s) that is (are) using similarpower. For example, if the additional service is a 4D1U data call, thenthe network finds four existing voice call users that use fourconsecutive timeslots with similar power requirement to the additionalnew remote station 123-127. If there is no such match, the network canreconfigure the timeslot and ARFCN to make a match. Then the networkassigns the four timeslots to the new data call which needs 4D TCH. Thenew data call also uses a different TSC. In addition, the uplink powerfor the additional one may brought to be close or to equal the uplinkpower of the remote station 123-127 already using the timeslot.

Assign a Remote Station 123-127 More than One TSC

If considering data services which use more than one timeslot, all (whenit is even) or all but one (when it is odd) of the timeslots may bepaired. Thus, improved capacity may be achieved by giving the remotestation 123-127 more than one TSCs. By using multiple TSCs, the remotestation 123-127 may, in one example, combine its paired timeslots intoone timeslot so that the actual RF resource allocation may be cut byhalf. For example, for 4DL data transfer, suppose that the remotestation currently has bursts B1, B2, B3 and B4 in TS1, TS2, TS3 and TS4in each frame. Using the present method, B1 and B2 are assigned one TSC,say TSC0, while B3 and B4 have a different TSC, say TSC1. The, B1 and B2may be transmitted on TS1, and B3 and B4 may be transmitted on TS2 inthe same frame. In this way, the previous 4DL-assignment just uses twotimeslots to transmit four bursts over the air. The SAIC receiver candecode B1 and B2 with TSC0, and B3 and B4 with TSC1. Pipeline processingof decoding the four bursts may make this feature work seamlessly withconventional approaches.

Combining Timeslots

Combining one user's even number of timeslots may halve the over the air(OTA) allocation, saving battery energy. This also frees additional timefor scanning and/or monitoring of neighbor cells and system informationupdate for both serving cell and neighbor cells. There are some furtherfeatures on the network side. The network may make the additionalassignment of co-channel, co-time slot (co-TS) based on the distance ofthe new users. Initially the network may use the TCH whose users are ata similar distance. This can be done through timing TA of each user.Each user's RACH provides this info to the BS 110, 111, 114.

Changes in Network Traffic Assignment

The above also means that if two co-channel, co-TS users are moving indifferent directions one moving towards the BS and the other moving awayfrom the BS, there will be a point that one of them will switch toanother TCH that has a better match of the power level. This should notbe a problem, as the network may be continuously re-allocating the userson different ARFCN and TS. Some further optimization may be helpful,such as optimizing selection of the new TSC to be used, as this isrelated with the frequency reuse pattern in the local area. Oneadvantage of this feature is that it uses mainly software changes onnetwork side. e.g., BS and BSC. Changes on network traffic channelassignment may increase the capacity.

Co-channel operation for both voice and data

Further improvements may be made. First, Co-TCH (co-channel andco-timeslot) may be used for voice calls as well as for data calls onthe same TCH to improve capacity-data rate. This feature may be appliedto GMSK modulated data services, such as CS1 to 4 and MCS1 to 4.8 PSK.

Fewer Timeslots Used

This feature may be applied to a reuse of co-channel (co-TCH) on datacalls to achieve increased capacity. Two timeslots of data transfer maybe paired and transmitted using one timeslot with two training sequencesused in each of the corresponding bursts. They are assigned to thetarget receiver. This means that 4-timeslot downlink may be reduced to a2-timeslot downlink, which saves power and time for the receiver.Changing from 4-timeslot to 2-timeslot operation gives the remotestation more time to do other tasks, such monitoring NC, which willimprove the hand off (HO).

The constraints of assignments with respect to Multi-slot Classconfiguration requirements such as Tra, Trb, Tta, Ttb—Dynamic andExtended Dynamic MAC mode rules may be relaxed. This means that thereare more choices for the network to serve the demands from variouscallers in the cell. This reduces or minimizes the number of deniedservice requests. This increases the capacity and throughput from thenetwork point of view. Each user can use less resources withoutcompromise of QoS. More users can be served. In one example, this may beimplemented as a software change on the network side, and remote station123-127 is adapted to accept additional TSCs on top of its DARPcapability. The changes on the network traffic channel assignment mayincrease the capacity-throughput. Use of uplink network resources can beconserved, even while the network is busy. Power can be saved on theremote station 123-127. Better handover performance and less restrictionon network assigning data calls, and improved performance can beachieved.

Dual Carrier

The present method and apparatus may be used with dual carrier inaddition, to improve performance. Dual carriers are allocated from whicha remote station can receive signals on two channels simultaneously inorder to increase the data rate. The apparatus and methods describedherein may be used with dual carrier to improve performance on thedownlink.

New TSCs

The present method and apparatus provide an improvement to existing DARPcapable components so that the network is able to use the co-TCH, i.e.co-channel frequency (the ARFCN that is already in use) and co-timeslot(the timeslot that is already in use), to serve additional users andprovide extra services by assigning different TSCs to the differentremote stations 123-127 which can therefore use the same channel whenthe remote stations are in communication with a single base station.With a more advanced SAIC receiver it is possible to give a second,third or even fourth user communication service on the same ARFCN andtimeslot. One feature used for improving capacity is to use multipleTSCs on the co-TCH, i.e. if two users/services share the same TCH, thentwo TSCs are used; if three users/services share the same TCH, thenthree TSCs are used and so on. The methods disclosed above may be usedto advantage for GERAN voice/data calls, for example.

Using SAIC of a DARP capable receiver for multi-users on one slot of thepresent method and apparatus, two different training sequences are usedfor two remote stations sharing the same channel. Characteristics of thetraining sequences that are evaluated are auto-correlation andcross-correlation. Of these, cross-correlation is particularly useful tothe present method and apparatus. The DARP function performs well withgood cross-correlation. The cross-correlation of two training sequencescan be viewed as a measure of mutual orthogonality. In simple terms, themore mutually orthogonal two training sequences are, the more easily theremote station's 123-127 receiver can distinguish one training sequencefrom the other training sequence.

Cross-correlation is quantified by means of a parameter known ascross-correlation ratio. If two training sequences are totallyuncorrelated (which is an ideal condition never achieved in practice),then the cross-correlation between the training sequences is nil and thecross-correlation ratio for the two training sequences is zero.

By contrast, if two training sequences are perfectly correlated (whichis the worst condition for co-channel operation and for DARP operation),then the cross-correlation between the sequences is maximized and thecorrelation ratio for the two training sequences is unity, i.e. equal toone.

It is possible to use two different existing training sequences shown inTable 4 to distinguish users in a MUROS call. Table 4 lists the existingeight training sequences for existing GSM systems identified in section5.2.3 of technical specification document 3GPP TS 45.002 V4.8.0(2003-06) entitled “Technical Specification 3rd Generation PartnershipProject; Technical Specification Group GSM/EDGE Radio Access Network;Multiplexing and multiple access on the radio path (Release 4)”,published by the 3rd Generation Partnership Project (3GPP)standards-setting organization.

However to use only the existing eight training sequences would reduceeight stand alone training sequence sets for frequency planning to fourpaired training sequence sets, which may restrict frequency planningTherefore, the present patent application identifies the following twonew sets of training sequences which can work with existing trainingsequences defined in the GERAN specification. The new sets are sets oforthogonal training sequences, each new sequence orthogonal with atleast one of the eight existing training sequences (i.e. the newsequence and an existing sequence having low cross-correlation andhaving a low correlation ratio). Existing training sequences can be usedfor legacy remote stations, while the new set of training sequences maybe used for new remote stations capable of executing this new feature.

The new training sequences have particularly advantageous correlationproperties making them suited for use in a GSM implementation of thepresent method and apparatus. The new sequences have been specificallychosen to pair with existing sequences shown in Table 4. The newsequences are listed in Tables 5 and 6 below, and are described in moredetail in the following text. While the present method and apparatuswould operate satisfactorily where the two sequences used for channelsharing are chosen from the existing set (shown in Table 4 below), ithas been determined that better performance can be obtained by means ofthe definition of, and use of the new, complementary sequences astraining sequences in combination with the existing training sequences.

Therefore, in one example, applying the present method and apparatus toa GSM system, a base station 110, 111, 114 transmits both a first signalhaving a first training sequence and a second signal comprising a secondtraining sequence which is a new training sequence complementary to thefirst training sequence. For example, the base station 110, 111, 114transmits a first signal having a first training sequence identified bya code TSC0 (from Table 4) and a second signal comprising a secondtraining sequence identified by a code TSC0′ (from Tables 5 or 6), whichis a new training sequence complementary to the first training sequenceTSC0. The cross-correlation ratio between the first training sequenceand the second, complementary new training sequence is very low. As aresult of this low cross-correlation, the performance of the DARPreceiver has been found to be particularly favorable when the first andsecond training sequences are used for two signals receivedsimultaneously by the DARP receiver. The DARP receiver can betterdistinguish between the first and second signals and can betterdemodulate the first signal while rejecting the second signal, ordemodulate the second signal while rejecting the first signal, dependingupon which of the two training sequences has been allocated for theremote station 123-127 to use for communication.

The new sequences have cross correlation ratios of between 2/16 and 4/16when correlated against a corresponding existing training sequence. Theuse of the additional new sequences delivers a further advantage,whereby more sequences are available for use in each cell or sector,giving more flexibility and fewer constraints on cell planning.

FIG. 35 is a flowchart illustrating a method of transmitting two signalson a single channel comprising a single frequency and a single timeslot. The method includes: generating (block 3502) a first trainingsequence from a first set of training sequences; and generating (block3513) a second training sequence from a second set of trainingsequences. The first and second training sequences have a lowcross-correlation ratio with respect to each other; and the second setof training sequences is different from the first set of trainingsequences. A first data is generated (block 3503). A second data isgenerated (block 3513). The first data is combined (block 3504) with thefirst training sequence to produce first combined data and the seconddata is combined (block 3514) with the second training sequence toproduce second combined data. The first combined data is, in thisexample, modulated onto a carrier to produce a first signal. The secondcombined data is, in this example, modulated onto a carrier to produce asecond signal. The first and second signals (containing first and secondcombined data respectively) are transmitted (block 3530) on the singlechannel by a single transmitting apparatus. Optionally the first andsecond signals are combined (block 3520) prior to being transmitted(block 3530).

It is noted that the new training sequences can also give performancebenefits when used for signals transmitted by the remote station 123-127to the base station 110, 111, 114. The base station 110, 111, 114,having a receiver which has DARP capability or similar advancedperformance, can better distinguish between two signals which itreceives on the same channel, each signal transmitted by a differentremote station 123-127. During a call, both the downlink signal for thecall, transmitted by the base station 110, 111, 114, and the uplinksignal transmitted by the remote station 123-127, will typically havethe same sequence (as is the case for GSM).

As stated above, table 4 shows the set of eight existing trainingsequences used for the GSM system. The training sequences are labeledTSC0 to TSC7. Each training sequence has 26 bits (bit 0 to bit 25). Inall of these training sequences, the first five and the last five bitsof a training sequence are repeated versions of five bits elsewhere inthe training sequence. For example, the five most significant bits ofthe TSC0 training sequence (bits 21 to 25) are 00100, and these bits arerepeated at bits 5 to 9. The least significant bits of the TSC0 trainingsequence (bits 0 to 4) are 10111, and these bits are repeated at bits 16to 20. Because of this repetition, it is usual to assign a short-handnumber to each training sequence, the short-hand number being defined asthe decimal value of the word formed by bits 5 to 20 inclusive, althoughthe number could alternatively be represented in hexadecimal (hex) form.Thus, the serial number for TSC0 is 47172 decimal, or B844 hexadecimal(hex) as shown in the table.

The training sequences shown in Table 4 are listed in section 5.2.3 oftechnical specification document 3GPP TS 45.002 V4.8.0 (2003-06)entitled “Technical Specification 3rd Generation Partnership Project;Technical Specification Group GSM/EDGE Radio Access Network;Multiplexing and multiple access on the radio path (Release 4)”,published by the 3rd Generation Partnership Project (3GPP)standards-setting organization and further discussed in technicalspecification document 3GPP TS 45.005 V4.18.0 (2005-11), entitled“Technical Specification 3rd Generation Partnership Project; TechnicalSpecification Group GSM/EDGE Radio Access Network; Radio transmissionand reception (Release 4)”, also published by the 3rd GenerationPartnership Project (3GPP) standards-setting organization.

TABLE 4 Training Sequence Training Sequence Code Bit 26 . . . 0 DEC HEXTSC 0 00100 1011100001000100 10111 47172 B844 TSC 1 001011011101111000101 10111 48069 BBC5 TSC 2 01000 0111011101001000 0111030536 7748 TSC 3 01000 1111011010001000 11110 63112 F688 TSC 4 000110101110010000011 01011 23683 5C83 TSC 5 01001 1101011000001001 1101054793 D609 TSC 6 10100 1111101100010100 11111 64276 FB14 TSC 7 111011110001001011101 11100 57949 E25D

Table 5 shows a preferred set of new training sequences complementary tothose shown in Table 4, for use according to the present method andapparatus. Each new training sequence is for use in combination with theone of the existing training sequences. The new complementary trainingsequences are labeled TSC0′ to TSC7′. TSC0′ is for use in combinationwith the TSC0, TSC1′ is for use in combination with the TSC1, and so on.In applying the present method and apparatus, a base station 110, 111,114 transmits on the same channel both a first signal having a firsttraining sequence (for example TSC0 ) and a second signal comprising asecond training sequence (e.g. TSC0′) which is complementary to thefirst training sequence.

TABLE 5 Training Sequence Training Sequence Code Bit: 26 . . . 0 DEC HEXTSC 0′ 01111 1100110101001111 11001 52559 CD4F TSC 1′ 011001111110010101100 11111 64684 FCAC TSC 2′ 01110 1101111010001110 1101156974 DE8E TSC 3′ 01101 1110100011101101 11101 59629 E8ED TSC 4′ 111101101110001011110 11011 56414 DC5E TSC 5′ 01010 1100111111001010 1100153194 CFCA TSC 6′ 01101 1100101000001101 11001 51725 CA0D TSC 7′ 111001101010011111100 11010 54524 D4FC

A further set of new training sequences having suitable properties isshown in Table 6. These training sequences are for use with theircorresponding training sequences from Table 4 as explained above.

TABLE 6 Training Training Sequence Sequence Code Bit: 26 . . . 0 DEC HEXTSC 0′ 01111 1100110101001111 11001 52559 CD4F TSC 1′ 011011100010111101101 11000 50669 C5ED TSC 2′ 00101 1110110111000101 1110160869 EDC5 TSC 3′ 11110 1101110001011110 11011 56414 DC5E TSC 4′ 011001111110010101100 11111 64684 FCAC TSC 5′ 01010 0000110111001010 000013530 DCA TSC 6′ 01000 0101110001001000 01011 23624 5C48 TSC 7′ 111001011111011111100 10111 48892 BEFC

Improved co-channel rejection performance is obtained if the pairingsare used for the two co-channel signals, shown in Table 7. Each newtraining sequence shown in Table 7 can be from either Table 5 or Table6.

TABLE 7 Existing New training training Pairing sequence sequence A TSC 0TSC 0′ B TSC 1 TSC 1′ C TSC 2 TSC 2′ D TSC 3 TSC 3′ E TSC 4 TSC 4′ F TSC5 TSC 5′ G TSC 6 TSC 6′ H TSC 7 TSC 7′

Alternatively, adequate performance may be obtained by using any of thefollowing pairings: Any two training sequences from Table 4; Any twotraining sequences from Table 5; Any two training sequences from Table6; Any two different training sequences from any of Tables 4 to 6.

Thus, steps for using the new training sequences are as follows:

When MUROS mode is enabled for the two users, at least one of them areMUROS and DARP capable remote station 123-127, which has the knowledgeof new training sequences.

The working pattern may be selected to be 0-0′, 1-1′ . . . , 7-7′,However, other combinations beside using a training sequence and itscompliment work well also. For example 1-2, 1-2′ may work. However, itmay be better to use a training sequence from Table 4 and its complementsuch as 1-1′ and 2-2′. This is due to DARP iterative process, which canadapt to the change of code.

It is desirable for the training sequences to be different, so that thecross-correlation is low.

Using the additional training sequences results in minimal, if any,changes implemented on the remote station 123-127 side unless additionaltraining sequence codes are to be defined. Using additional trainingsequence codes are an improvement of the present co-TCH method andapparatus.

The impact on the remote station 123-127 side is:

Define new set of orthogonal training sequence codes. Existing trainingsequences can be used for legacy remote stations, while the new set oftraining sequences may be used for new remote stations 123-127 capableof executing this new feature.

Thus, in addition to being DARP capable, the remote station 123-127supports the new training sequence codes also.

The impact on the network side is:

The network assigns two different training sequences to the co-TCHusers. If new training sequences are defined, then the network mayassign these to remote stations 123-127 supporting a new trainingsequence set and assign legacy training sequences to legacy remotestations 123-127.

FIG. 15 is a flowchart illustrating the steps taken with the presentmethod. Following the start of the method 1501, a decision is made instep 1502 as to whether a new connection is required between the basestation 110, 111, 114 and a remote station 123-127. If the answer is NO,then the method moves back to the start block 1501 and the steps aboveare repeated. When the answer is YES and a new connection is required,in block 1503 a decision is made as to whether there is an unusedchannel (i.e. an unused time slot for any channel frequency). If thereis an unused time slot on either a used or an unused channel frequency,then a new time slot is allocated in block 1504 on that used or unusedchannel frequency. The method then moves back to the start block 1501and the steps above are repeated.

When eventually there is no longer any unused time slot (because alltime slots are used for connections), the answer to the question ofblock 1503 is NO, and the method moves to block 1505. In block 1505 aused time slot is selected for the new connection to share with anexisting connection which is already using that time slot.

A used time slot on a channel frequency having been selected for the newconnection to share along with an existing connection, a complimentarytraining sequence (complimentary to the training sequence used by thecurrent user of the slot) for the new connection is then selected inblock 1506, and the new connection is initiated. The method then movesback to the start block 1501 and the steps above are repeated.

The present methods disclosed in this patent application may be storedas executable instructions in software 961 stored in memory 962 whichare executed by processor 960 in the BTS as shown in FIG. 16. They mayalso be stored as executable instructions in software stored in memorywhich are executed by a processor in the BSC. The remote station 123-127uses the training sequence it is instructed to use.

New Proposed Sets of TSCs: QCOM7+QCOM8

As stated above, two new sets of training sequences, QCOM7+QCOM8, havebeen identified which may work with the above existing trainingsequences identified in the GSM specification. QCOM7 corresponds toTable 5 and QCOM8 corresponds to Table 6. The two new sets of sequencesare proposed to for future MUROS operation. The pairings are:

Training sequences identified in the GSM/EDGE specification with QCOM7training sequences, and training sequences identified in the GSM/EDGEspecification with QCOM8 training sequences.

There are some duplications of training sequence bits in the two groups.Both groups perform well when paired with training sequences identifiedin the GSM/EDGE specification. As discussed above, when MUROS mode isenabled for the two users, the working pattern may be selected to be:0-0′, 1-1′ . . . , 7-7′.

Table 8 is a Test Configuration Summary of parameters used when runningtests using the new sets of training sequences and the legacy trainingsequences. FIGS. 17-18 contain test results, and FIGS. 19-34 areperformance plots.

TABLE 8 Test Configuration Summary E_(b)N_(o) 26 TDMA Frames 20,000 RSSIthreshold −103 dBm Fixed or Floating Floating point Logical ChannelAHS5.9 Mode Traffic Path Terristial Urban Speed 3 ^(km)/_(h) CarrierFreq 900 MHz Freq Hopping Enabled Ratio of Desired to Interference 0 dB(2^(nd) user) Phase difference between desire & 90° interference (2^(nd)user) Desired user Signal based on QCOM 7 or QCOM 8 TSC Interference(2^(nd) user) Signal based on Legacy TSC

Signaling for the Assigning of Additional Training Sequence Codes

Currently, according to the prior art, there are eight trainingsequences defined and, as described above, these training sequences areused to provide separation between different users across differentcells rather then different users within the same cell.

By contrast, according to MUROS operation, each cell has the ability fortwo training sequences to provide separation of two users within thesame cell. In MUROS at least one new set of eight training sequences isdefined. The remote station indicates to the network (via the BS) if itsupports the new training sequence set. The existing signaling messagescontain three bits to tell the remote station which of the eighttraining sequences to use for the communication link. The signalingmessages are enhanced so that the remote station can also be signaledwhich of the two sets of training sequences to use.

According to the present method and apparatus, a mechanism is definedfor signaling the training sequence set information to the remotestation with no increase in size of the signaling message itself.

FIG. 36 is a flowchart comprising steps taken by a base stationaccording to the present method and apparatus to identify capability ina remote station to operate using new training sequences. The remotestation signals to the network if it supports a new set of trainingsequences via a mechanism such as Classmark 3 signaling. (See step 1710of flowchart in FIG. 36). Once the network knows that the remote stationsupports more than one set of training sequences for a communicationchannel, then the network can decide which set of training sequences theremote station shall use for the communication channel beingestablished. According to the present method and apparatus the existinginformation element called Channel Description (defined in 3GPP TS44.018 section 10.5.2.5) is modified to signal the training sequence setto be used by the remote station for the communication channel beingestablished. (See step 1720 of flowchart in FIG. 36). The ChannelDescription has a 5 bit field called Channel type and TDMA offset. Thepresent coding of Channel Type and TDMA offset field is as follows:

TABLE 9 8 7 6 5 4 0 0 0 0 1 TCH/F + ACCHs 0 0 0 1 T TCH/H + ACCHs 0 0 1T T SDCCH/4 + SACCH/C4 or CBCH (SDCCH/4) 0 1 T T T SDCCH/8 + SACCH/C8 orCBCH (SDCCH/8)

As can be seen from the coding of Channel Type and TDMA offset fieldthat fifth bit (in bit position 8) always has a value of 0.

The present method and apparatus makes use of the fifth bit to indicatewhich training sequence set the mobile device is to use for the trafficchannel. The advantage of this method and apparatus is that reliabilityof this information is consistent with existing control messages and thechange is made in one place in the specification to cater for all thecircuit switched assignment messages.

The proposed new coding of Channel Type and TDMA offset field is asshown in Table 10 below.

TABLE 10 8 7 6 5 4 S 0 0 0 1 TCH/F + ACCHs S 0 0 1 T TCH/H + ACCHs S 0 1T T SDCCH/4 + SACCH/C4 or CBCH (SDCCH/4) S 1 T T T SDCCH/8 + SACCH/C8 orCBCH (SDCCH/8)

The S bit indicates the training sequence set to use as follows:

S 0 The legacy training sequence set to be used 1 The alternative/newtraining sequence set to be used.

If a remote station does not support the alternative/new trainingsequence set and bit S is set to 1 then the remote station shall returnan ASSIGNMENT FAILURE with cause “channel mode unacceptable”.

A further implementation of the invention will now be described whichallows a single base station and a single remote station to send andreceive signals to each other to support two calls (each for data orvoice).

In this implementation the base station signals training sequence setinformation to a remote station. The signaling comprises firstlyreceiving signaling from the remote station, the received signalingindicating whether a new set of training sequences is supported by theremote station. The base station uses a channel description to signalthat a first training sequence set is to be used by the remote stationfor a first communication channel being established and that a secondtraining sequence set is to be used by the remote station for a secondcommunication channel being established, the first and second trainingsequence sets comprising any two of the legacy, QCOM 7 and QCOM 8training sequence sets (shown in Tables 4, 5 and 6 respectively).

Both the base station and the remote station transmit and receive firstand second combined signals (comprising first and second trainingsequences respectively as described above) on the same channel. In thisway, the same remote station can maintain two calls with the single basestation on a single channel, whereas, as described previously above,each of the two calls were maintained by two different remote stations.

In order to implement the above feature, extra signaling information isrequired from the base station to indicate to the remote station that ituse both training sequences on the same channel. Also, the remotestation must be adapted, as described above for a base station, toproduce and combine two signals for each of two respective data streamssuch that the remote station may transmit the two signals on the samechannel, the signals intended for the single base station.

For example, the Channel Type and TDMA offset field may be adapted sothat, during one transmission of the Channel Type and TDMA offset field,the above-described signal is transmitted indicating the trainingsequence set to be used by the remote station for the communicationchannel being established. During a second transmission of the ChannelType and TDMA offset field, the extra signaling information, to indicateto the remote station that it use both training sequences forcommunicating on the same channel, is transmitted.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted as one or more instructions or code on a computer-readablemedium. Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The methods described herein may be implemented by various means. Forexample, these methods may be implemented in hardware, firmware,software, or a combination thereof. For a hardware implementation, theprocessing units used to detect for ACI, filter the I and Q samples,cancel the CCI, etc., may be implemented within one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, electronic devices, other electronicunits designed to perform the functions described herein, a computer, ora combination thereof.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples described herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

Those of ordinary skill in the art would understand that information andsignals may be represented using any of a variety of differenttechnologies and techniques. For example, data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof.

Those of ordinary skill would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a Digital SignalProcessor (DSP), an Application Specific Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in Random Access Memory (RAM), flashmemory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM),Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal. In thealternative, the processor and the storage medium may reside as discretecomponents in a user terminal.

Therefore, the present invention is not to be limited except inaccordance with the following claims.

The invention claimed is:
 1. A method of transmitting two signals on asingle channel comprising a single frequency and a single time slot, themethod comprising: generating a first training sequence from a first setof training sequences, wherein a training sequence is a known sequencetransmitted in a signal in a time slot burst; generating a secondtraining sequence from a second set of training sequences, the secondtraining sequence being different from the first training sequence, thefirst and second training sequences having a low cross-correlation ratiowith respect to each other; and the second set of training sequencesbeing different from the first set of training sequences; generatingfirst data; generating second data; combining the first data with thefirst training sequence to produce first combined data; combining thesecond data with the second training sequence to produce second combineddata; and transmitting on the single channel by a single transmittingapparatus a first signal comprising the first combined data and a secondsignal comprising the second combined data, wherein the singletransmitting apparatus is part of a base station; the first and secondsignals are for respective first and second remote stations; and thesingle base station serves the first and second remote stations.
 2. Amethod according to claim 1, further comprising: receiving a signalindicating that the second set of training sequences is supported by aremote station.
 3. A method according to claim 1, further comprising:transmitting a signal comprising a channel description indicating thatthe second set of training sequences is to be used by the remote stationfor a connection.
 4. A method according to claim 3, wherein: the channeldescription has a channel type field and a TDMA offset field; thechannel type field and TDMA offset field comprising: 8 7 6 5 4 (bitnumber) S 0 0 0 1 TCH/F + ACCHs S 0 0 1 T TCH/H + ACCHs S 0 1 T TSDCCH/4 + SACCH/C4 or CBCH (SDCCH/4) S 1 T T T SDCCH/8 + SACCH/C8 orCBCH (SDCCH/8),

wherein the bit numbered 8, with a variable value of S shown, indicatesthe training sequence set to use, wherein TCH/F indicates a full ratetraffic channel, wherein TCH/H indicates a half rate traffic channel,wherein ACCH refers to an associated control channel, wherein SACCHrefers to a slow associated control channel, wherein SDCCH refers to astandalone dedicated control channel, and wherein CBCH refers to a cellbroadcast channel.
 5. A method according to claim 4, wherein eachsequence of the first set of training sequences has a complementarysequence in the second set of training sequences which provides thelowest cross-correlation ratio with respect to the sequence of the firstset of training sequences.
 6. A method according to claim 5, wherein:the first set of training sequences (TSC0 to TSC7) comprises: 001001011100001000100 10111 (TSC 0) 00101 1011101111000101 10111 (TSC 1)01000 0111011101001000 01110 (TSC 2) 01000 1111011010001000 11110 (TSC3) 00011 0101110010000011 01011 (TSC 4) 01001 1101011000001001 11010(TSC 5) 10100 1111101100010100 11111 (TSC 6) 11101 111000100101110111100 (TSC 7);and the second set of training sequences comprises either:01111 1100110101001111 11001 (TSC 0′) 01100 1111110010101100 11111 (TSC1′) 01110 1101111010001110 11011 (TSC 2′) 01101 1110100011101101 11101(TSC 3′) 11110 1101110001011110 11011 (TSC 4′) 01010 110011111100101011001 (TSC 5′) 01101 1100101000001101 11001 (TSC 6′) 111001101010011111100 11010 (TSC 7′) or 01111 1100110101001111 11001 (TSC 0′)01101 1100010111101101 11000 (TSC 1′) 00101 1110110111000101 11101 (TSC2′) 11110 1101110001011110 11011 (TSC 3′) 01100 1111110010101100 11111(TSC 4′) 01010 0000110111001010 00001 (TSC 5′) 01000 010111000100100001011 (TSC 6′) 11100 1011111011111100 10111 (TSC 7′).
 7. A methodaccording to claim 1, further comprising combining the first and secondsignals to produce a combined signal and transmitting the combinedsignal.
 8. A method according to claim 1, wherein the second trainingsequence is used for signals transmitted by a remote station apparatus.9. An apparatus for transmitting two signals on a single channelcomprising a single frequency and a single time slot, the apparatuscomprising: means for generating a first training sequence from a firstset of training sequences, wherein a training sequence is a knownsequence transmitted in a signal in a time slot burst; means forgenerating a second training sequence from a second set of trainingsequences, the means for generating first and second training sequencesbeing configured to generate the first and second training sequencessuch that the second training sequence is different from the firsttraining sequence, the first and second training sequences have lowcross correlation ratio with respect to each other, and the second setof training sequences is different from the first set of trainingsequences; means for generating first data; means for generating seconddata; means for combining the first data with the first trainingsequence to produce first combined data; means for combining the seconddata with the second training sequence to produce second combined data;means for transmitting on the single channel by a single transmittingapparatus a first signal comprising the first combined data and a secondsignal comprising the second combined data, wherein the apparatus ispart of a single base station; and the apparatus is configured to serverespective first and second remote stations and to transmit the firstand second signals for the respective first and second remote stations.10. An apparatus according to claim 9, the apparatus further comprising:means for receiving a signal indicating that the second set of trainingsequences is supported by a remote station.
 11. An apparatus accordingto claim 10, further comprising: means for transmitting a signalcomprising a channel description indicating that the second set oftraining sequence is to be used by the remote station for a connection.12. An apparatus according to claim 11, the apparatus configured totransmit the signal so that the channel description has a channel typefield and a TDMA offset field, the channel type field and the TDMAoffset field comprising: 8 7 6 5 4 (bit number) S 0 0 0 1 TCH/F + ACCHsS 0 0 1 T TCH/H + ACCHs S 0 1 T T SDCCH/4 + SACCH/C4 or CBCH (SDCCH/4) S1 T T T SDCCH/8 + SACCH/C8 or CBCH (SDCCH/8),

wherein the bit numbered 8, with value of S shown, indicates thetraining sequence set to use, wherein TCH/F indicates a full ratetraffic channel, wherein TCH/H indicates a half rate traffic channel,wherein ACCH refers to an associated control channel, wherein SACCHrefers to a slow associated control channel, wherein SDCCH refers to astandalone dedicated control channel, and wherein CBCH refers to a cellbroadcast channel.
 13. An apparatus according to claim 12, wherein themeans for generating the first and second training sequences areconfigured to generate the first and second training sequences so thateach sequence of the first set of training sequences has a complementarysequence of the second set of training sequences which provides thelowest cross-correlation ratio with respect to the sequence of the firstset of training sequences.
 14. An apparatus according to claim 13,wherein the means for generating the first and second training sequencesare configured to generate the training sequences such that: the firstset of training sequences (TSC 0 to TSC 7) comprises: 001001011100001000100 10111 (TSC 0) 00101 1011101111000101 10111 (TSC 1)01000 0111011101001000 01110 (TSC 2) 01000 1111011010001000 11110 (TSC3) 00011 0101110010000011 01011 (TSC 4) 01001 1101011000001001 11010(TSC 5) 10100 1111101100010100 11111 (TSC 6) 11101 111000100101110111100 (TSC 7);and the second set of training sequences comprises either:01111 1100110101001111 11001 (TSC 0′) 01100 1111110010101100 11111 (TSC1′) 01110 1101111010001110 11011 (TSC 2′) 01101 1110100011101101 11101(TSC 3′) 11110 1101110001011110 11011 (TSC 4′) 01010 110011111100101011001 (TSC 5′) 01101 1100101000001101 11001 (TSC 6′) 111001101010011111100 11010 (TSC 7′) or: 01111 1100110101001111 11001 (TSC0′) 01101 1100010111101101 11000 (TSC 1′) 00101 1110110111000101 11101(TSC 2′) 11110 1101110001011110 11011 (TSC 3′) 01100 111111001010110011111 (TSC 4′) 01010 0000110111001010 00001 (TSC 5′) 010000101110001001000 01011 (TSC 6′) 11100 1011111011111100 10111 (TSC 7′).15. An apparatus according to claim 9, further comprising means forcombining the first and second signals to produce a combined signal andwherein the means for transmitting is arranged to transmit the combinedsignal.
 16. An apparatus according to claim 9, further comprising areceiver for receiving signals transmitted by a remote station, thesignals comprising the second training sequence.
 17. An apparatus,comprising: a processor; a memory in electronic communication with theprocessor; and instructions stored in the memory, the instructionsexecutable by the processor to: generate a first training sequence of afirst set of training sequences, wherein a training sequence is a knownsequence transmitted in a signal in a time slot burst; generate a secondtraining sequence of a second or a third set of training sequences, thesecond training sequence different from the first training sequence,each of first and second training sequences having a low crosscorrelation ratio with respect to the other training sequence; generatefirst data; generate second data; combine the first data with the firsttraining sequence to produce first combined data; combine the seconddata with the second training sequence to produce second combined data;and transmit on a first channel comprising a single frequency and asingle time slot, by a single transmitting apparatus, a first signalcomprising the first combined data and a second signal comprising thesecond combined data, wherein the apparatus is part of a single basestation; and the apparatus is configured to serve respective first andsecond remote stations and to transmit the first and second signals forthe respective first and second remote stations.
 18. A remote stationapparatus comprising: means for generating a training sequence of afirst or a second set of training sequences; means for generating data;means for combining the training sequence with the data to providecombined data; means for transmitting on a single channel comprising asingle frequency and a single time slot a signal comprising the combineddata; means for transmitting a capability signal indicating that boththe first and second sets of training sequences are supported by theremote station; means for receiving a signal comprising a channeldescription indicating that the second set of training sequences is tobe used; the means for generating the training sequence configured sothat the generated training sequence is from the second set of trainingsequences depending on the channel description indication.
 19. Anapparatus for operating in a radio communications system, the apparatuscomprising: a data source for supplying a first and second data fortransmission; at least one sequence generator for generating a firsttraining sequence and a second, different training sequence, wherein atraining sequence is a known sequence transmitted in a signal of a timeslot burst; a combiner for combining the first training sequence withthe first data to produce first combined data and for combining thesecond training sequence with the second data to produce second combineddata; and a transmitter for modulating and transmitting both the firstand the second combined data using the same carrier frequency and thesame time slot, wherein cross-correlation ratio between the firsttraining sequence and the second, complementary new training sequence isvery low, wherein the apparatus is part of a single base station; andthe apparatus is configured to serve respective first and second remotestations and to transmit the first and second signals for the respectivefirst and second remote stations.
 20. The apparatus as claimed in claim19 wherein the first training sequence is complementary to the secondtraining sequence.
 21. The apparatus as claimed in claim 19 wherein saidat least one sequence generator is a plurality of sequence generators.22. A non-transitory computer readable medium comprising instructionswhich when carried out by a computer perform the method of claim 1.